Blood Relative by David Thomas

Peter Crookham runs a very successful architectural practice with his German-born wife, Mariana. One afternoon he arrives home from work to find Mariana covered in blood--it appears that she has murdered Peter's brother, Andy. Peter and Mariana are taken to the police station, but soon Peter is let go and Mariana is put in a psychiatric hospital, because it seems that she's suffered some type of psychotic breakdown. Peter realizes that if he can uncover the motive behind Andy's death he'll be able to find out if Mariana is guilty. Peter's investigation leads him to look into Mariana's youth in what was then East Germany. Blood Relative is a thriller in the style of Harlan Coben and keeps the reader guessing until the end.