CoC - Advice on bringing investigators together

Hey! I'm planning to run a short CoC RPG, about 2-3 sessions with a group of friends, which are all RPG veterans with Gurps/DnD.

My current issue is to bring all of them together as they are quite different characters from each other, one being a Student at Misk University, one a Psychiatrist and the other one a Police officer.

How do you generally get them to work together? Got any tips? I was trying to avoid something too obvious or rail roaded.