The House of the Red Slayer (The Sorrowful Mysteries of Brother Athelstan, #2)

The Constable of the Tower of London, Sir Ralph Whitton, is found murdered in a cold, bleak chamber. The door is still locked from the inside and guarded by trusted retainers—so how did the assassin get in? And why was Sir Ralph so terrified by a message he received a few days before his death?