Long Lost, Harlan Coben

Myron is summoned to Paris at the behest of an old lover, Terese. She is in unspecified trouble and needs his help. When he gets there, he discovers that her husband has been murdered and she is the main suspect. The interesting thing is that more than one blood-type has been discovered at the scene - and the other blood can only be attributed to her daughter. But she died 10 years before.

As Myron and Terese try to find out exactly what's going on, they uncover more and more questions. Did the daughter really die? Did Terese's husband have a further child with someone else?

But the truth is something no one expected...