In case (of)

from English Grammar Today

In case is a conjunction or adverb. In case of is a preposition.

In case

We use in case to talk about things we should do in order to be prepared for possible future situations:

Shall I keep some chicken salad for your brother in case he’s hungry when he gets here? (conjunction)

In case I forget later, here are the keys to the garage. (conjunction)

She knows she’s passed the oral exam, but she doesn’t want to say anything just in case. (adverb)

We don’t use in case to mean ‘if’.

Compare

Let’s take our swimming costumes in case there’s a pool at the hotel.	We don’t know if there is a pool there.
Let’s take our swimming costumes ifthere’s a pool in the hotel.	We will wait until we know about the pool before we decide.

I’ll take cash in case we need it on the ferry. (we don’t know if we will need cash on the ferry)

In case of

We use in case of + noun to mean ‘if and when something happens’:

[notice in a lift]

In case of breakdown, please press the alarm button and call this number. (if and when the lift breaks down, …)