Let the players make up all that stuff!
How about letting the players fill the rest of the exposition? So following from your quote:
Wilma: (shouts) "I'll cover you. GO!" I turn dive behind the garbage cans in the alley, drawing my gun. That first goon is going to have a nasty shock. The rest will get suppression fire.
Craig: (over comms) "Debbie, turn left on the freeway! We'll hijack a car."
Debbie: (over comms) "No, we're close to Clown territory, if we get there we can get backup and come back for Wilma. Follow me!" I jump and head straight for the backstreet with the Clown markings.
Here you are allowing the players to come up with interesting ideas about what and how things unfold. You can then incorporate whatever was made up into your game.
I started several games just like that: No one had characters, states, or background: just names and a situation. Things moved on from there as they described themselves, what they were doing, and what skills they had.
The main rules we had were don't be a dick and never knowingly contradict someone else's story. These are fairly simple really. Also, because you are creating the world as you go, whatever you say is what happens. So, it's best to leave things open ended and not closed. So, in your example, what would be the point of Wilma saying "I take out my nuke grenade and blow the alley so the buildings collapse(1)." In that respect, an idea of what style and themes you wanted to play helps: is it a gritty noire cyberpunk setting or a super hero show a la Arrow/Flash/Daredevil?
One of the games we ran several times started with
You are at a wake.
That was it! No setting, no 'nuffing. Everything was build up from the ground up. Try it next time you have a couple hours to kill with your group.
As mxyzplk stated in a comment:
This gets to the heart of it. A real narrative game is one where the
exposition isn't required because it's collaboratively generated.
Tacking a single narrative technique on an otherwise simulationist
game will be more problematic.
The first point is indeed spot on.
As to the second point, it still work even in a simulationist game if your idea of role playing is building a collaborative story where both GM and Players have input as to where the story goes and generate content on the fly. On the other hand, if the GM does not allow this and/or treat the game as a "GM vs Players", then in medias res cannot work as the players are denied full knowledge of the situation. Clearly, if the characters lack said knowledge, that would work as Nvoigt's fine answers suggest.
(1) Although, I can think of a fun game based off that too!
Ask "How do you do that?"
Players do things by describing their actions. "I want to investigate the room for odd books" is not an action, it's a desirable goal. An action would be:
- "I browse through every book on these shelves, until I find something like a spellbook"
- "I start tapping the walls, trying to find a hiding place"
- "I look under the bed. What do I see there?"
- "I glance at the table. Do I see any odd-looking books there?"
- ... other statement which gives insight about time, efforts and possible risks
Whilst describing a goal could be useful for determining the outcome, the general framework still states "players describe what they want to do", not "what they want to achieve". This is exactly how the rules describe the game process, see PHB page 6 "How To Play":
- The DM describes the environment.
- The players describe what they want to do.
- The DM narrates the results of the adventurers' actions.
"I investigate" is a valid action too, although it is very broad and vague. Adding "for X" doesn't make it clearer, unfortunately. When in doubt, a DM is free to ask for clarifications from players.
Don't rush with dice rolls
When players say they want to "investigate", that doesn't automatically mean they have to make an Intelligence (Investigation) check, or any kind of ability check at all.
What you're talking about is probably the "I use X skill" mentality, which came from previous versions (3.x primarily).
It assumes that a player states the exact skill she is using, then she states the goal she wants to achieve, then a dice roll is necessary using the mentioned skill modifier:
"I want to disable this trap using my Disable Device skill!" (rolls the dice)
This is not how 5e works anymore. 5e has no skill checks for a reason. Instead, players describe their actions, then the DM describes the outcome. A DM doesn't have to ask for a dice roll. PHB suggests to roll dice only "where the outcome action is uncertain", and the DMG goes even further:
One approach is to use dice as rarely as possible. Some DMs use them only during combat, and determine success or failure as they like in other situations.
With this approach, the DM decides whether an action or a plan succeeds or fails based on how well the players make their case, how thorough or creative they are, or other factors.
More specific example
So, let's say the party searches for an ancient grimoire. The party enters a room, then a player states "I want to investigate for odd books". What happens next depends on the multitude of factors. What do they do, exactly? What can be found here? Is there any time limit? Are we talking about a deliberate hiding place, or is the room just untidy? And so on:
- If the room is a library, there're thousands of books here. "There are a lot of odd books here. How exactly are you going to find the proper one?" Maybe it's time to use the Locate Object spell, or ask NPCs, or do something else. Let your players be creative.
- If it's an empty cell, there are no books at all. You don't want to waste time on pointless dice rolls. "You see no books here, just cold stone walls and a crude trestle bed". Maybe players would investigate the bed — again, describe it without rolls and move on.
- A thorough search requires effort, but the party has plenty of time. On "How do you do that" they replied, "We leave no stone unturned until we find anything," so they will find all valuable things sooner or later, no dice roll is required. Just say what they did find. "You've spent a couple of hours and found an odd-looking spellbook and a sack of coins".
- If it's a living room with many things and time is the essence, the outcome is uncertain. "Okay, you want to search for books here. How do you do that? You probably have only a couple of minutes before the orcs arrive." Perhaps the player will say, "Okay, I want to rummage through shelves as quickly as possible." The risks and reward are clear, so you ask the player for a roll. The result is quite high but you know the book isn't there. "Well, you can't see any books here, but you've found an intriguing letter signed by Black Spider." Or, on a failed check: "In a rush, you accidently drop one of the shelves on the floor. Boom! You bet someone could hear this."
- Et cetera.
There can't be one "generic" answer, as there can't be a generic "Investigate the room" check in 5e.
Traps are a completely different topic
Speaking of traps, there is no silver bullet for them either. Moreover, making good traps is difficult, there are a lot of guides and videos on this topic. You can start with this one for example. Or watch this video.
Angry GM summarized the rolling part as "Only Roll When There is Chance of Success, A Chance of Failure, and A Risk or Cost of Failure" here (rule 2, hence Title Case). Being short and somewhat pithy helps me keep it in mind when GMing.
(kudos to @minnmass for the summary)
For instance, if you give players a chance to notice traps only when they explicitly say "I investigate the room for traps", they will probably say this in every room, and nobody will enjoy this. Instead, it might be a better option to use Passive Checks, or ask for a Wisdom (Perception) check right before the trap could spring.
Best Answer
System agnostic answer
Many roleplay games (D&D traditionally not among them) have the concept of "failing forward". This means that every roll has some consequence which is usually narrated by the GM and usually bad for the character or the party as a whole. A roll without possible negative consequences should not be made.
Examples of such rules are:
Burning Wheel has "Intent" and "Let it ride" rules. Intent is stated before every roll. When the roll succeeds, the intent happens. When the roll fails, all manners of things may happen (at GMs discretion) but the intent definitively doesn't happen. This can't be changed by any roll until the situation in fiction has significantly changed. An example of this two rules in play would be:
Apocalypse World has "moves" a GM (MC in Apocalypse World) can make when players fail a roll. The moves are of general nature ("take their stuff away", "separate them", "inflict harm") and don't have to be directly caused by the attempted action.
What that means for your situation
With the statue example this would mean that a failed roll would totally allow you to narrate the character springing the trap. He chose to investigate and thus took the risk of touching something, he shouldn't touch. If he insists on doing a "safe, no touch" investigation he most likely won't get much useful information (but also wouldn't have to roll).
Final advice
While some games support, encourage and even demand to be played like this, many games (including D&D) don't. Thus any attempt to start playing in this style has to be agreed upon with the whole group (trivially true when it is part of the official rules of the game being played). I strongly suggest shifting to "failing forward" as the alternative leads to very slow and static play-style where not much happens, nobody trusts one another and where there is constant rules lawyering.