a part in (something)

1. A specific involvement or participation in something; a role in some undertaking. There's no use lying to the committee, Mr. Marshall, as we know for a fact that you played a part in your company's decision to hide its losses from investors. Listen up, Joe. You're going to play a part in this operation, too. I had no part in this, Officer, I swear! I had no idea they were stealing money!

2. The role as a certain character in a performance, such as a theater or film production. I hear that Samantha got a part in the director's newest film! I bombed my audition and didn't end up getting a part in the play. Plenty of people go to Hollywood and never end up getting a part in anything.