Unlike both previously discussed titles, GUMSHOE is not a standalone game, but a quasi-generic role-playing game system underlying a number of games geared towards mystery and investigation plots, such as Trail of Cthulhu (2008), Night's Black Agents (2012), and TimeWatch (2017). Developed for Pelgrane Press by Robin D. Laws in 2007, GUMSHOE had originally been a proprietary system exclusive to Pelgrane's productions, but was released to the public for free in 2013.

Free resources: System Reference Document.

Core Mechanic

GUMSHOE has been designed to alleviate a specific issue pervasive in mystery-focused role-playing games: that of the PCs missing vital investigation clues due to bad luck at dice. Laws' solution was to eliminate the element of chance from the investigation procedure entirely (with the justification that the PCs are supremely competent in their respective fields of expertise) and shifting the gameplay focus away from obtaining evidence towards interpreting it. Because this only applies to the PCs' investigative abilities and not to general ones (like hand-to-hand fighting), however, GUMSHOE effectively has two core mechanics, a "Karma"-based for investigating and a "Fortune"-based one for everything else (to borrow the terms introduced by Laws' former co-author Jonathan Tweet in his 1995 Everway). For this survey, we are only interested in the investigative procedure, described on pp. 6-7 of the SRD:

  1. The player announces that their character is using a particular "investigative ability" to look for clues in the current (crime) scene.
  2. As long as the PC has at least one "point" invested in the stated ability, the GM reveals to the player all of the key information their character needs to advance the plot.
  3. The GM announces whether the PC can gain any "special benefits", such as additional clues, from the current scene with their chosen investigative ability, and how many points they cost.
  4. The player decides how many special benefits (if any) they purchase and "spends" the corresponding number of points from their ability, reducing its effective score until the next mystery.
  5. The GM reveals any additional clues or enacts in-fiction any special benefits that the player has purchased.

Interpersonal Abilities

The reason why we are only interested in the investigative core mechanic is that all but one of the primary stats that GUMSHOE classifies as "Interpersonal" fall under the investigative abilities. Consequently, the primary purpose of social interaction in this system is not to influence behavior, but to obtain information from NPCs. Interpersonal investigative abilities (pp. 8-26) can be further split into "parlances" and "techniques" (our terms):

  • Parlances are specialized vocabularies and norms that allow for effective blending in and communication with certain social classes or professions. Examples include "Authority", "Bureaucracy", "Cop Talk", "High Society", "Respect", "Streetwise", and "Tradecraft".
  • Techniques are specific modes of persuasive communication, such as "Charm" (optionally subdivided into "Flattery" and "Flirting"), "Inspiration", "Interrogation", "Intimidation", "Negotiation", "Reassurance", and "Taunt".

A special investigative technique called "Bullshit Detector" (p. 10) lets PCs recognize when an NPC lies to them. The only Interpersonal ability that isn't investigative but general is "Public Relations" (p. 32), which is used to maintain and to improve the PCs' social standing and credibility.

We observe that because of the system's heavy emphasis on mystery-solving, its only mode of social interaction involves PC agents interrogating NPC patients in various ways. It provides no explicit support for gaining compliance beyond revealing the sought-after information, nor for any of the "PC patient" configurations (like in Apocalypse World, in fact, the GM never rolls dice in this system).