fall in with

[fall in with] {v.}, {informal} 1. To meet by accident.

Maryfell in with some of her friends downtown.

2. To agree to help with;support.

I fell in with Jack's plan to play a trick on his father.

3. To become associated with a group detrimental to the newcomer.

John fell in with a wild bunch; small wonder he flunked all of hiscourses.

Compare: PLAY ALONG.