The Wormhole wrote:
Didn't Harriman resign from Starfleet at the end of Serpents or am I misremembering things? It has been a decade since I read it so that's certainly possible. Of course, given this book is set eight years after Serpents, that's plenty of time for Harriman to resign and then decide to return to Starfleet.
It's stated in one of the S.C.E. e-books (can't remember which) that Harriman served as liaison to the S.C.E. after he stepped down from command of the Enterprise.