A mouse in the house

If you know where they're coming in then plug the gap with some wire wool.

Definitely this and I would go further, ie actively look for any hole or gap to plug with steel wool and hold it in place with expanding foam. (Helps with insulation too)
If you have damp areas, invest in bronze wool instead so it won't rust.
These motherfuckers are not Beatrix Potter creations - kill them in the face with fire etc in the most convenient way for you.
I have had them staring me out in my garage and making pinging noises as they climb over bicycle wheels. I still shudder at the thought.
I had made the mistake of storing fat balls in there and they had chewed into a plastic bucket to get at them.
Final point - pull the fridge out and anything else that moves in your search for holes and keep everywhere scrupulously clean to remove food sources.