Sleuth Publications Ltd, 1986, any number of players, and pretty much any age. Gumshoe was SPL's follow-up to their mostly successful "Sherlock Holmes Consulting Detective" series of games (with the genre now being "Hardboiled 1930's San Francisco" instead of "Victorian London"). As in CD, the basics of a "case" are laid out in the clue book in narrative fashion. Then, it's up to the players to pluck the interesting details from said narrative. Once armed with a few avenues of inquiry, players then visit those people/places in order to find clues, evidence and further avenues of inquiry. As in the case set-up, clue points at a given location are laid out in narrative fashion. Once players feel that they have enough evidence to solve a given case, they then take a short test to see how they did.
As in CD, players have various references at their disposal (maps of San Francisco and surrounding areas, telephone directories, newspapers, autopsy/crime reports, fingerprint cards, etc).
Unfortunately, Gumshoe suffers from the same sort of "bloat" that plagued the later CD add-ons. Rather than simply presenting a series of small/self-contained cases that a group of players can comfortably solve in a single session, Gumshoe has dozens of interconnected mysteries, none of which can be adequately solved until you've gone through all of them. Gumshoe is played out over the course of nine days, with each new day introducing a new case. And each "day" in the game takes a literal day (or more) of playing time. So, if your group is like mine (getting together once a month), you're looking at close to a year of clue slogging before you can even begin to solve any of the cases. And good luck remembering all of the details from one session to the next!
Making matters worse, SPL totally hosed up the first edition of this game. So, don't even bother trying unless you have the second edition. Here's a transcript of a forum exchange discussing the issue that I came across while researching this game -
Ken - When I first went to work for Sleuth Publications, the 2nd edition of this game was just shipping out to stores to replace the unplayable 1st edition. Stores were supposed to return or destroy the primary edition, but I imagine not all were. So if you're ever about to purchase a copy, be sure to check the printing history.
Jeff - What exactly made the first edition unplayable, and how do you tell? I have a copy - can't even remember how I got it now - and couldn't find any mention of print history anywhere (the main clue book just has the 1985 copyright date).
Ken - If your copy isn't marked as a 2nd edition, then it's more than likely a 1st. The problem with the first edition was that you'd spend hours playing it, but something was left out so the game could not be completed. Since the 2nd edition was a complete reprint and not just an errata sheet or booklet added to 1st edition copies, I'm pretty sure it was a very big omission.