Kate Brennan left her job as a fifth-year associate at Dewey & LeBoeuf in June for a post in the general counsel’s office at one of the law firm’s best clients. Four months later she was back.

She wasn’t fired and she didn’t quit. Instead, Brennan’s departure and return were part of a secondment, an arrangement cooked up by the law firm, Brennan and the client, Ambac Assurance Corp. The idea was to staff the in-house counsel office with a bright associate who could go back to the firm after a few months with a better understanding of the client’s operations and needs. “It gave us a huge leg up,” Brennan said.