I'll start soon a Trail of Cthulhu game, and I know next to nothing about Lovecraft or even Cthulhu itself.
What I know is that this game is based more on investigation and discovery (my GM told me that the game would be a little less "horror" than the standard – even if i don't know what standard IS), therefore I like the fact that I genuinely don't know in advance what I'm going to face in game, because it'll help me impersonate my character better (I think it's something similar to watching the Star Wars saga for the first time, when you don't really know that Vader is Luke's father).
Nevertheless, I'm kind at a loss about what kind of game this is.
I've made some research: I know that the environment should be based around the 1930s United States, and I'm following the tips given in this question HERE. Also, I'll watch "The Untouchables" soon, but most of the other answers are either about game mechanics or about other aspects I don't want to discover out-of-game.
I know that this question may seem odd, and I guess that a part of it it's caused by my poor grasp of english (I'm not a native english speaker)
The question:
What should I expect from a game of "Trail of Cthulhu" as a player, which doesn't know anything about the game setting except for the time and place?
If possible keep the spoilers at minimum in your answers! I'm mainly interested to know what's the life expectancy of a character (D&D 4e VS Paranoia), how's the general "mood" of the environment (My little pony VS grimdarkness of warhammer 40k) and things like that (basically, everything that does not involve game mechanics, dice rolls, skill checks – if they exists – and so on). I am NOT looking for informations about Cthulhu itself or the "monsters" I may face (if there are monsters, that is)
I understand that my question may be unclear. I'm open to suggestion about how to improve it. Also, if you need to know more to answer properly, feel free to let me know and I'll try to expand my question as best as I can.
Background informations
I guess that you may find useful to know what my RPG background is: sadly, my only experience about played RPGs is limited to a couple/three years of D&D 3.5 played during high school (that means about 8 years ago). I played an elf ranger with longbow.
I am also currently plaing a warhammer 40.000 LARP, as a medic guardsman.
An example of what I'm looking for
Let's say I've asked this question about a warhammer 40k LARP instead of ToC. The correct answer would mention that each character have a low life expectancy, that there's a lot of combat where it's really possible to lose a limb or even die (and therefore you'd better be careful when you move around or fight, because you might get ambushed) but also that there are invisible, inner or personal enemies to fight, that wants to corrupt you and give you some benefits in exchange of your soul / humanity.
Also, you'd better NOT to trust anybody, because backstabbing and back talking is very common, and you'd better be prepared. You have the possibility to be anything from imperium factions, and during each game you can pursue whatever targets you want… but keep in mind that your officers and commissars are watching, and your life isn't worth as much as your equipment.
The environment is very, very reactive. Almost every action you take, a reaction will take place, sooner or later.
You'll face periods of intense work or fight that can be either very long or very short, with varying frequency during both day and night. There will be also long periods of quiet (but you can't tell how long it will last, so be prepared!) where you have some freedom to move on your own, but you're never, ever completely safe, even during lunch breaks or inside your faction's own base.
Fights may be deadly but still you have the chance to stand and fight if you have your companions: usually the enemy is too tough for an 1vs1. You may equip/spec yourself to handle some specific situation, but you can't ever be prepared for every possible situation, you're forced to rely on your companions to survive the campaign.
Best Answer
Trail of Cthulhu is based on the novels and the mythos inspired by H.P. Lovecraft's series of novels. I wouldn't spoil what the content of his novels specifically are, but in modern days it will be comparable with TV series such as X-Files and Supernatural, but in the 1930s.
In general, such games usually emphasis research and investigation, and tends to be gritty, though each group has it own lethality setting. Investigators are weaker than a 1st level character in any D&D game, and they do not just have to worry about their physical health, but their sanity as well. Indeed, a classic theme of the game is to trade your sanity for powerful occultic secrets that men are not intended to know. It is easy to get killed or to be driven insane, though that depends on the style of the game your group is running. You can run a Cthulhu-inspired game like a horror movie, or a with a more 'pulp' spin on it.
Though you did not ask for mechanics, I would like to mention one that makes Trail of Cthulhu unique. In the game you can always find core clues without rolling any skill, as long as you are trained in that area of investigation. You could ask to examine the body, and the GM will tell you any evidence you will need to further your investigation. Hence asking the right questions rather than "I search for anything unusual" is rather important.
Added on edit: Usually combat plays a smaller role in such games, and it will be esoteric knowledge, preparation and tactics that save the day, as the deck is usually stacked against you. Knowing what you are getting into and having the necessary protection against what you are up against is important.