After spending the night with Tim, Marcella goes to Henry for more information to help track down Matthew. Little does she know that Matthew is desperately trying to attract her attention from the cellar, where he is being held captive. She hears nothing, however, and tells Henry she thinks Matthew is the killer. After leaving, Henry viciously tells Matthew how his plan to frame him is working. But what will he do with Matthew now? At the police station, Rav wants to focus on Yann and Matthew as suspects, but Marcella is suspicious that Henry didn't seem to know that Matthew couldn't have moved Grace. Surely he knew about his best friend's back problems? Marcella looks into Henry's alibi for the night of Grace's murder. Mark traces his phone to a pub, where it turns out there was a break-in that night. It could have been Henry... Marcella confides in Jason about her suspicions and enlists him to help her snoop around Henry's office. She manages to download documents which reveal Henry had access to Matthew's diary, so knew his whereabouts exactly...