An Heir And In The Same Breath Regret

(AU backstory warnings at the beginning of every chap) One day, Kevin Ryan goes for lunch. Nobody knows where he's gone or why, but when he returns, something is different. Nobody, not his friends, not his partner, not even his wife knows what's going on. Then a murder comes across their desks, and they're thrown into a past nobody knew about, one that should have been left alone.