From beyond the grave

After the death of his father, Charley Du Monceau – a wealthy computer scientist – received a memoir from his notary that incriminating his mother-in-law. According to this diary, his stepmother was responsible for the deaths of his mother and father. Furious, Charley files a complaint against his mother-in-law for double homicide and gives the diary to the police as evidence. However, his stepmother disappears the same day, and so does the memoir. Could this be a settling of scores? Has Charley decided to take the law into his own hands as the police claim or is he only serving as a diversion for the real kidnapper?