The Family Remains by Lisa Jewell

Early one morning on the shore of the Thames, DCI Samuel Owusu is called to the scene of a gruesome discovery. When Owusu sends the evidence for examination, he learns the bones are connected to a cold case that left three people dead on the kitchen floor in a Chelsea mansion thirty years ago.
Rachel Rimmer has also received a shock—news that her husband, Michael, has been found dead in the cellar of his house in France. All signs point to an intruder, and the French police need her to come urgently to answer questions about Michael and his past that she very much doesn’t want to…