Luyện ngữ pháp - English Grammar in Use - Intermediate ((Unit 114: In case))
Study this example situation:
Your car should have a spare wheel in case you have a puncture.
In case you have a puncture = because it is possible you will have a puncture.
In case is not the same as if. We use in case to say why somebody does (or doesn't do) something. You do something now in case something happens later.