Trollkiller: Viking Detective (tentative title)

Here's the basic guts of an indie-game I've been working on. It's still in its infancy, so any feedback or ideas are appreciated.

SYNOPSIS:
You (PCs) are a trollkiller. You kill trolls in middle-ages Europe.

There are 4 types of trolls. War, Famine, Plague, and Eclipse. Trolls eat people. When they eat enough people, they cause a localized apocalypse of their name-sake. To cause an apocalypse, a troll will terrorize one village or city until it has eaten enough people to bring the village or city to ruin. You and your fellow trollkillers have come to stop this. Unfortunately, no one will help you. Trollkillers are outsiders (Normans, moors, albinos, Mongols, armed women, pagans). Everyone hates you, suspects you of the grisly things happening, and would like to burn you at the stake. Fortunately, you bear the heraldry of a respected northern kingdom. Because of this you are allowed to bear arms at all times, but are afforded few other knightly considerations.

Your goal is to use detective work to find the troll, then kill it, before it eats its 10th victim and causes a localized apocalypse.

INVESTIGATION:

Trolls don’t just eat anyone, they have specific tastes:
-War troll eats the courageous as the cowardly.
-Famine troll eats the temperate and indulgent.
-Plague troll eats the young and the elderly.
-Eclipse troll eats the heartbroken and the newly enamored.

Trollkillers must interview witnesses and friends/family of the victim to ascertain facts about the victims. By process of elimination, the trollkillers discover what type of troll they are after. For instance, the trollkillers hear that a lord has gone missing. Upon investigation, they learn that the victim is a young lord who just returned from battle to marry the woman he has been courting. That victim could be on the menu of the War (couregous), Plague (young), and Eclipse (newly enamored). More victims will give more clues and narrow the field. Once the troll killers have discovered what type of troll they are dealing with, it’s time for the stakeout.

STAKE OUT:

During the day, trolls ride the wind invisibly and whisper to people. They don’t just whisper to anyone, however:
-War trolls whisper to nobles and commoners.
-Famine trolls whisper to farmers and traders.
-Plague troll whispers to healers and the sick.
-Eclipse troll whispers to priests and heretics.

Trollkillers must watch the Whispered-To carefully. The whispered-to are tormented and threatened by trolls. They act as accomplices to the trolls’ late night sneaking and kidnapping. They unlock gates, cause distractions, and obscure trails. They have no choice. However, their torment begins to manifest quickly. If the trollkillers know who to watch, they’ll be able to learn clues about the nature of the troll. Some practices of the whispered-to include self-mutilation, cruelty to animals, irrational fears, and obsession with nature. Each of these symptoms betrays a fact about the troll. For example, a whispered-to cuts himself = the troll is immune to blades. A whispered-to who catches and kills birds = a spirit eagle will guide the trollkillers to the troll’s mound once they know where to look. Like the previous lists of prefered victims and whispered-to's, this series of clues and their manifestations will be known to the players.

THE HUNT:

Hunt will be phased, and operate like a Friday the 13th Movie. Basically, the trollkillers must split up and try to flank and flush the troll into a spot where all 3 or 4 trollkillers can engage the troll at once (as 1-on-1 with a troll is suicide for even the strongest of trollkillers). Players will go round the table making their hunt rolls (whether they are sneaking, searching by torchlight, or leading dogs). Once the table gets X number of successes, they have pinned and engaged the troll. However, each time a player rolls and gets no successes, there is a TROLLSTRIKE! Trollstrike is a brutal troll attack on one trollkiller (picked randomly). He must defend himself until his fellow trollkillers arrive. When the party arrives, the troll flees and its back to the drawing board. 3 trollstrikes in one hunt means that the troll escapes, day breaks, he turns invisible, and he’ll be eating 1 more victim before next hunt.

TIME LIMIT:
When the troll eats 10 people, it causes an apocalypse. A Plague troll will cause a deadly plague to ravage the city. An eclipse troll will cause mass hysteria where the denizens of the city kill one another. Etc. Game over (unless there is campaign play of some type).

Trollkillers will be lead to a tormented town or city by a spirit guide. Depending on how fast they get there, 1 to 3 people have disappeared (and been eaten by a troll). Every night, there is a new victim, regardless of how the trollkillers operate (even if they somehow mobilize the entire city to prepare for a trollstrike).

Each day (or rather, day + night), each PC has the option of investigating one death or doing a stake-out on one whispered-to, or joining in a hunt. Of course, you'll want to finish the investigation before doing a stake-out, and finish the stake-out before doing the hunt.

BTW, trollkillers kill trolls not just cuz' its their job. Fact is, they have troll heritage themselves. If they don't break the curse (by killing trolls!) they become a troll... a fate worse than death.

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I've a lot more ideas written down, but that's the short version. Gritty detective work + the Middle Ages + Trolls + Vikings. Narrow focus, explicit goal, time limit, and our detective PCs will know exactly what clues they are looking for. So some questions:

1) First impressions?

2) I was thinking of using a traditional basis (stats, skills, weapons) for the construction of PCs, but then funneling these PCs through the Investigation/Stake-Out/Hunt phases during play... a sort of "directed play." Skills would aid in clue finding (example: "my Threaten skill will make the peasant tell me everything he knows about the night of the killing," "my Smith skill will let me break into the antechamber and see what this priest has been doing," and of course, troll killing. Does this sit right with folks?

3) Any tips on murder mystery gaming? The only mystery game I've ever played is Clue, so I'd appreciate any recommendations. The basis for our viking detectives will be Troll Lore aka What the Player's Know about Trolls. There will be no Occult rolls and no forensics... to succeed, trollkillers will have to watch people and hear stories about the dead. In fact, players will have a special Clue Sheet that they'll all contribute to.

1) As far as first impressions I'd say that it looks like fun. An interesting concept and I like the focus.
2) I'd think that a traditional method of character building would be OK, but make since the game is so focused it might end up that everyone picks one or two things to be really good at and as a team they're good at everything. This sounds good, even desirable, but if someone doesn't show up for a game the group might end getting the shaft. Although if it's focused on more of one session thing then this wouldn't really be an issue.
3) No real experience in mystery gaming, but making it have more than a single die roll is important to keep up the tension. Wearing down peoples wills can be just as, if not more, exciting than a battle if played out right. Another thing is that if you have PC's staking out places it would be logical for them to do this separately in order to cover more ground, bu the problem then is that if everyone but one person has a false lead then that person could end up doing something interesting (and possibly dangerous) all by themselves with no group input, so I guess you could try and think of something to deal with that.
Overall, I'd say go for it! Looks like a fun idea to me.
One last thing though- you implied that if the PCs fail then its kind of like a "game over" scenario- but are you planning to have rules/ suggestions on running an adventure during/after a disaster? A lot of those sound like they'd make great adventure hooks in themselves, and apocalypses like a war wouldn't exactly get resolved quickly. I could see the PCs having to find some sort of cure- but such a thing would inevitably come at a high price. That sounds like an opportunity for some real drama.

Thanks for the feedback.

In response to your response #3:

False leads or "red herrings" are a crucial aspect to the murder mystery genre of fiction. Most murder mysteries are an open-shut case, but it is the false leads and red herrings that continue to confound the reader and make them question their own instincts. As a GM for traditional "chuck dice/kill shit" campaigns, I've been able to employ red herrings to decent dramatic effect. However, as a fundamental aspect to the murder mystery genre, I'd like to give red herrings their own substantial emphasis (or mechanic) in this murder mystery game, instead of leaving this maneuver up to GM fiat.

Then again, I wonder if red herrings are already built into the Investigation phase. If the first three victims are youths, the players are likely to do stake-outs to a Plague Troll's whispered-to. It might lead to a dead end, punctuated by the next death, which is the death of a middle aged man. Suddenly, its not a Plague Troll there after, and they are 1 victim closer to the apocalypse. Back to the drawing board: what actually connects the victims now?

Addressing the "splitting up" aspect of the Stake Out phase, this is a legitimate concern. As a GM and player, I've always felt uncomfortable with splitting up the party, because it meant that some players may have to sit and watch longer than they are happy with. I have a dilemma: should a GM engage a dead-end Stake-Out as a legitimate story element (thus reinforce the red herring aspect), or should dead-ends stop before they start so all the party members can be involved in the real Stake-Out? I guess I'm partial to the former. I have no problem introducing some minor fantasy elements to the game to give players a means of calling for back up (I mean, these dudes fight TROLLS, and are guided to troubled cities by an elusive white elk, or something). That might be the trick.

Addressing your last comment:

Currently, I've been building the game with the assumption that a Trollkiller campaign is a short, contained story about killing 1 Troll and preventing 1 apocalypse. Long campaign rules would assume that: 1) detectives would increase or decrease in power over time, dictated by their success rate killing trolls, and 2) that there is a definitive endgame beyond the localized apocalypse, such as Failure) trollkillers become trolls or Success) killing Grendel's mother. I was thinking of incorporating Troll Blood as part of each detectives heritage... and Troll Blood would increase with each apocalypse, and decrease with each beheaded troll. While Troll Blood could be used to activate sweet abilities (super strength, regeneration), it would mostly be a measure of how successful the campaign has been, and how close it is to the endgame.

Chad,
  This game has a lot of potential, but what separates it from the Milton Bradley game, "Guess Who?"
  I feel like the awesome is right there in front of me, but I just wonder if actual play will drift towards a sort of mechanical process of elimination instead of a more puzzling mystery, does that make any sense?
  Either way, good luck man!

Good questions and good points. I guess there isn't a lot that separates the investigation phase of Trollkiller from the elimination method of "Guess Who?" In Trollkiller, however, its not a matter of just asking another player questions... the trollkillers would actually have to find out these things through play. They would have to interview the friends and family of the victims who are bereaved and would likely paint the victim's nature in an angelic light. They would also interview witnesses, who know something they don't want to tell to anyone (such as what was the victim REALLY doing in the barn? Practicing witchcraft? Having an inappropriate affair?). Not only that, but the trollkillers are outsiders (barbarians, albinos, armed women, moors, Mongols), meaning that they face serious social obstacles while they search for the truth. (Setting wise: it will be understood that Trolls are impervious to "Christianized Magick," and thus, most trollkillers are outsiders.)

What would keep the investigation phase from becoming mechanical instead of puzzling? I have no clue! It's true that players would likely come up with ingenious ways to sift through the victims and identify the Troll type rapidly. I haven't playtested yet, so I need to confirm if the current method is too easy or too obtuse in actual play. Either way, the investigation is only 1/3 of the full mystery/story. I currently have things set up so that the players know all the Troll lore they'd need to solve the mystery. The reason for this is simple: I want it to be a fair environment between GM and players. The player's shouldn't have to "pixel bitch" (a term used to describe clue hunting in old PC adventure games) each scene, and the GM should never have to spell it all out for the players who are getting bored and agitated.

Perhaps some type of "Complication" could be added to the mix at the beginning of each mystery. For example, "branded as heretics" might make the trollkillers hunted by inquisitors while they are doing their job. Perhaps the Trollkillerrs know of the possible complications before play, but don't know which one is active.

I'm totally open to ideas, here.

Chad,
  One thing rubs me the wrong way though:
1) The TrollKillers are outsiders (I get that and its cool)
2) The TrollKillers will become Trolls if they don't redeem themselves (I get that and its cool)
3) But, why are they monkeying around with Viking culture if they are outsiders and why do they espouse viking traditions (courage, etc), if they are not their own traditions?
  Once that is resolved, I think the game will really firm up in your mind...

  Also, maybe the GM should have the Right/Privilege/expectation to monkey around with one of the Troll Traits before the mystery begins. Like Maybe all War Trolls Feed on Courage, the Young and Nobles (this is just a simple example, I know your lore is more complex). BUT, the GM has the ability to switch up one of those before the scenario starts, so you could have a War Troll that feeds on Courage, the Dying and Nobles. And that adds an unknown element to the mix that the players have to puzzle out, even if they have the lore memorized, no?

  Anyways, seems like a cool game, good luck man!