Do capítulo introdutório:
[quote=Kenneth Hite]Why This Game Exists
This game exists in order to adapt the greatest RPG of all time, Call of Cthulhu, to a different rules set, the GuMSHoE engine. Why on Earth would we do a thing like that? First of all, part of what makes Call of Cthulhu so great is its theme, taken from the cosmic despair of the greatest horror writer of the 20th century, HP Lovecraft. We kept that. Second, part of what make Call of Cthulhu so great is its deliberate decision to make characters increasingly vulnerable to the horrors they face, to give their bravery real meaning and force real mechanical consequences in the game. We kept that, too.
So what did we change? Let me change the subject. The greatest playwright ever is William Shakespeare. His greatest play is King Lear. Why would Akira Kurosawa make that play into a movie? And why would he set that movie, Ran, in samurai-era Japan instead of quasi-ancient Britain? Because more people want to – or can — see a movie than a play, and because transferring the story to Japan makes its themes paradoxically clearer than leaving them in the “familiar” world Shakespeare wrote. Did Ran improve on King Lear, or make it obsolete? Don’t be ridiculous. Did it do something worth doing by changing King Lear? Absolutely.
To return to our topic, then: Another part of what makes Call of Cthulhu so great is its emphasis on investigation, on gathering clues instead of treasure. We designed GuMSHoE to make that easier, clearer, and more direct. GuMSHoE exists to solve a problem that many people found with running Call of Cthulhu – one bad die roll can derail an adventure. You didn’t find the diary, so you didn’t get the spell, so either Arkham is destroyed or the Keeper has to scuttle ‘round and plant the diary somewhere else. In Trail of Cthulhu, the GuMSHoE rules guarantee that you will find that diary. (We don’t promise not to destroy Arkham.) This is not the entirety of what GuMSHoE offers, but it was the starting point for GuMSHoE’s laser-like focus on investigation.
Some Keepers, and even some players, enjoyed seeing everything go pear-shaped, and reveled in the creative destruction of the adventure. Some didn’t, and worked out their own ways around the problem, ways they are perfectly happy with; their own crib sheets to King Lear, if you will. We hope there is enough other good stuff in here for them, but Trail of Cthulhu is first and foremost for the Keepers and players who privilege investigation, and who want mechanics that do likewise. It’s for fans of procedural shows like House or CSI, in which the mystery isn’t “will the lab test come back,” but “what do the results mean”? That’s not to say things won’t go wrong for the players, merely that the wrongness won’t be caused by an absence of clues, but how they use them. It’s for players who are curious about the Call, and who want to follow the Trail all the way to the end.[/quote]