in the swim

in the swim  {adj. phr.}

Doing the same things that other people are doing; following the fashion (as in business or social affairs); busy with what most people are doing.

Jim found some college friends at the lake that summer, and soon was in the swim of things.

Mary went to New York with introductions to writers and artists, and that winter she was quite in the swim.

Contrast: OUT OF THE SWIM.