I’m running a 5e campaign, and our group is going into a period of the campaign that will likely involve a lot of ‘sneak in sneak out’ encounters/series of encounters, like assassination missions or thievery.
The problem is, I’m not sure how to keep it balanced with the so-called ‘adventuring day’; it seems like if they plan it well, or even if they don’t, they should have at most two fights in a row, and those in very quick succession, because they can hardly sneak in, have two fights in a row, rest for an hour (!!) without being caught, and then have two more.
How can I fit infiltration-style encounters or quests into the combat framework of D&D 5e?
(NB: I’m afraid the system is more or less non-negotiable; there’s a pandemic, and even if there wasn’t, we’re a good few levels into the campaign; it just wouldn’t work to change up systems.)
As requested in the comments, the party consists of two rogues and a Circle of the Moon druid, all at 3rd level.
Best Answer
A combat is just a way of draining resources
While most of the rulebook concentrates on how many combats you can manage in a single day the reality is that each combat is simply a way that the game gets the player characters to expend a certain amount of resource.
The idea is that at the end of each day they have used up those resources, and need to rest to regain them before they can move on.
You can do exactly this with other encounters.
Sneaking into a place can be as simple as 'make a Dexterity (Stealth) check to slip past the guard' which uses no resources and reduces infiltration to a matter of selecting the correct skill at character creation. I find that boring, and leads to what you worry about which is that a good roll leads to success and a poor roll leads to being caught potentially more dangerous than they would otherwise be capable of dealing with.
What I do is try and fill the path they take with other encounters which are aimed at draining resources, and with methods of achieving rest.
Encounters
For example: "You spend some time watching the patrol routes of the guards and realise that it simply isn't possible to sneak in using the rooms and corridors. However you spot a series of grates which you believe lead to an underfloor heating system, if you could get down there the grates in each room could potentially allow you to infiltrate almost anywhere in the building"
The players thus have to go under the building to sneak in, and you can fill that with traps, obstacles, gelatinous cubes or whatever else you think appropriate intended to use the same resources as a few combats.
The end result is they get to the same place within the building, but it took resources and skill rather than a single good roll, and they are less likely to get caught by every guard in the building.
You can achieve the same result by ensuring they reach a junction in the building and have to go left to avoid the guards, this will put them into a non-combat resource draining encounter.
Resting
If the group are under the building they can rest as they see fit, but once they go into the house that is a different story. However now they know there are ways to get under the house, maybe distracting the enemies, quickly killing them or filling the room with fog will allow them to simply disappear and the guards will be left wondering where they went. Failure could lead to the guards spotting and following, but you are in control of this so could simply make the players worry about being followed, but actually you have no intention of allowing it (if you run games in that way).
Alternatively; the guards would just want to capture them, and you could plan for them to be locked up for a while which gives them the chance to have a short rest and them look to escape. Which is always an adventure in itself.
TL/DR
Don't think of combat as the only thing that the party can encounter in a day, you can drain resource in other ways.
Don't let people potentially achieve a goal with just a good roll.