The Horror
I Know What You Did Last Summer was essentially a Scooby Doo murder mystery, but instead of a monster mask unveiling, it featured a hook-wielding serial killer. It all starts with a shared secret, a horror trope that experienced a resurgence after the Scream series. This sort of scenario works best as either a one short or if all the characters begin the campaign with the understanding that they have a dark secret. For fun, consider not sharing the secret right with the players at all because the characters refuse to discuss it.
There are a few staples of this genre, all part of a series of twists: 1) The murdered person isn't dead. 2) The murdered person's identity isn't who the characters think it is. 3) The person seeking revenge toys with each witness, attempting to kill them off one by one, often in gruesomely appropriate and/or ironic ways. For a one shot, it's easy to add archetypes to this sort of genre:
The Skeptic: This character is perfectly happy keeping the secret and has no interest in unearthing the past. There's a reason for this – revealing the secret might ruin him. It could be a highly public business, a career in the movies, or political aims. Whatever the case, the Skeptic wants the secret to stay buried and might even cover up evidence of the resurrected killer until he can "deal with it" on his own terms. This is, of course, a fatal mistake.
The Neurotic: A character wracked with guilt over the accident. The neurotic works well in games that feature a sanity mechanic. Whatever the rules system, he's the most mentally vulnerable of the bunch. The killer knows this of course and can use it to his advantage by manipulating the Neurotic into crying wolf several times before making an appearance.
The Investigator: The hero, which is probably most player characters. This archetype believes any outlandish murder plot and attempts to stop it by being well-armed. There's nothing wrong with this, but it might warrant having the other conspirators be non-player characters so they can crack under pressure at the right time.
The Stoner: Like the Neurotic, only he sublimates his guilt with drugs or alcohol. The Stoner is an unreliable witness and therefore equally likely to cry wolf or ignore evidence due to his proclivities for mind-altering fun.
The Love Interest: There's usually a couple in these sorts of scenarios, which is in itself a vulnerability for the group. This person is the one character the protagonist can trust. Or can he? She may be the real killer, or the slasher may try to drive a wedge between the couple my framing her for the crime.
For repeated fun, the first time the killer shows up it might be the accident survivor who was mangled in some creative way (losing his hand, face mutilated) from the incident. After he's killed, the second masked iteration could be his child. And the third time? That's when the original killer returns as a zombie out for revenge.
Your Turn: Have you ever used a shared guilt murder mystery in your game?
Looking for more gaming inspiration? Buy Mike's book about The Evolution of Fantasy Role-Playing Games, read his fantasy novel inspired by his role-playing campaign, or follow him on Facebook and Twitter.
