Below is a guide to the various lines of GUMSHOE products, arranged by date of initial publication. I've provided a brief description of the premise and what new ideas this iteration brings. As well, you'll find a link to the core book for the system, reviews for that core book, and links to other products in that line. In the case of Trail of Cthulhu, I've provided a link to the Gamer's Guide to that RPG.
Pelgrane Press has used their GUMSHOE rpg engine across a number of game lines. The mechanics of that system uniquely focuses on mysteries and problem solving. Not a generic system, GUMSHOE instead has a set of base mechanics and ideas tweaked, shifted and added to for each version- aiming to offer the best genre emulation.
For more game overviews, see the RPG System Metageeklist.
GUMSHOE is a ability-based system, with characters being defined primarily by the abilities they possess. Characters have two types of abilities: investigative and general.
Investigative abilities include fields of knowledge such as Ballistics, Forensic Anthropology, and Streetwise. These have a rating which serves as a pool for use of that ability. Possessing at least a one rating shows the character has expertise. When a player uses that ability to examine a scene, they do not have to roll. Instead, if there are core clues present which can be found by that means, they locate them. Points may be spent from an investigative ability to gain additional or extra information, at the GM or player's suggestion.
General abilities cover areas where players can risk failure- Athletics, Health and Shooting for example. Use of these abilities is uncertain and success or failure can have a dramatic impact on the story. General abilities also have a rating which represents a pool. To make a test, players roll 1d6. If they wish they may make a spend from the relevant ability's pool and add that to the roll. Players must meet or beat a difficulty set but not revealed by the GM. General ability pools require special circumstances to refresh (end of a story, time in a hospital, etc).
Review: GUMSHOE: RPGs I Like
Premise: Players take the role of agents for the Ordo Veritas, a benevolent conspiracy. They battle against the Esoterrorists, a network of radicals and maniacs dedicated to breaking down the membrane between this world and the supernatural outside. They do this by crafting terror and manifesting otherworldly creatures. They operate like a terror network, with a focus on fear and publicity.
System Additions: This book sets up the basic GUMSHOE rules, with expert agents operating in a modern setting. Pelgrane plans to publish a second, revised edition of this game.
Core Book: The Esoterrorists
Additional Products: The Esoterror Fact Book, Profane Miracles, Albion's Ransom: Little Girl Lost, Six Packed, The Book of Unremitting Horror
Core Book Reviews: The Esoterrorists: RPGs I Like and Review Of The Esoterrorists By Pelgrane Press
Premise: Players take the role of characters, perhaps victims, in a modern horror setting of slashers, creatures and maniacs. Fear Itself aims to simulate modern pop horror, especially cinematic horror of movies like The Ring, Pulse, and House of Wax.
System Additions: The list of abilities has been modified to reflect the lower relative skills of characters in this setting. The rules also include very basic psychic powers- with dangers associated with those. Characters can start from a list of stereotypes, and/or choose special Risk Factors- drives which explain why the character remains in the story rather than fleeing. Additional rules for stability appear as well.
Core Book: Fear Itself
Additional Products: The Book of Unremitting Horror, Invasive Procedures
Core Book Review: Fear Itself: RPGs I Like
Trail of Cthulhu
Premise: Investigators against the Cthulhu Mythos. Adapts the key ideas of Lovecraft's work and the rpg traditions established by Call of Cthulhu into GUMSHOE. ToC notably moves the timeline forward, setting the game generally in the 1930's, rather than 1920's.
System Additions: Retooled ability sets to fit the genre. The rules offer two approaches to campaigns and mechanics, Purist versus Pulp, with the latter offering the players more of a fighting chance. Characters now have Drives which guide their behavior and choose a Occupation to start. Occupations determine starting abilities, credit rating and special talents. Stability has now been paired with Sanity as two distinct abilities. Those rules, including madness mechanics, have been expanded.
The rules offer a significant discussion of the Cthulhu Mythos, followed by an extensive bestiary for creatures from there and elsewhere. Rules for setting-specific magic and tomes appear as well.
Core Book Reviews: Hiking with Cthulhu, Trail of Cthulhu: RPGs I Like, A perfect marriage of setting & rules, and My Profane Thoughts
Trail of Cthulhu: System Guide for New Gamers
Share A Game - Trail of Cthulhu
Mutant City Blues
Premise: An event ten years ago resulted in 1% of the population gaining super powers. Players take on the role of officers with powers dealing with "heightened" crime and criminals. A predictable structure and pattern to the superpowers allows for investigations based on meta-forensics.
System Additions: An extensive set of super-powers, some of which operate as investigative and some as general abilities. Unlike other superhero games, powers must be chosen along certain lines. These lines make up "The Quade Diagram" a resources for players to figure out which powers associate with which evidence. Other abilities and rules focus on the police procedural nature of the game.
Core Book: Mutant City Blues
Additional Products: Hard Helix, Brief Cases
Core Book Reviews: Mutant City Blues: RPGs I Like
Premise: A far-future sci-fi setting in which players take the roles of "Lasers," freelance law enforcers. These operate in the Bleed, a region of space once controlled by an empire known as the Combine, now left to its own devices. Navigating between disparate planetary cultures and races, the Lasers balance ethics and the need to make a buck. Moves the idea of mysteries forward more broadly to problem-solving.
System Additions: Several alien races with special talents provided. Alien specific abilities and psionics, as well as an ability list tuned to the sci-fi setting. Cyberware and biological implant rules. Extensive systems for spaceship combat. Notes on handling improvised investigations.
Core Book: Ashen Stars
Additional Products: Dead Rock Seven
Core Book Reviews: Review & A Couple of Thoughts, Ashen Stars - A review, and Stars Like Ash
Premise: Not a stand-alone core book, Lorefinder adds elements of GUMSHOE's investigative rules to the Pathfinder system.
System Additions: Character creation within Pathfinder; drives for PCs; and new skills, feats and magic
Core Book: Lorefinder
Core Book Reviews: Is that GUM on my Pathfinder’s SHOE? Or, can an “old” dog learn new tricks?
Night's Black Agents
Note that the final version of this game has not yet been released. A pre-order is available, allowing purchasers a pdf version of the rules without art or layout.
Premise: Players take the role of spies who have been "burned" by their company. The reason: their discovery of a massive vampiric conspiracy behind the scenes. Now the PCs must remain alive while striking back at the monsters.
System Additions: Highly tailored set of abilities for the genre- with new ideas and uses for abilities. Rules for using investigative abilities and general and vice versa. Benefits for high level purchases of general abilities. Role specific talents. Mechanics for trust, contacts, networks and betrayal. Now options for cinematic combat. Chase rules. Vampire and conspiracy construction toolkit.
Core Book: Night's Black Agents
Core Book Reviews: I'm a secret agent there's nowhere you can hide and Tinker, Tailor, Vampire, Spy