Original Sin (1) - S7.E1

Scotland Yard's Commander Adam Dalgleish is asked by Gabriel Dauntsey of the Peverell Press to look into an anonymous poison pen letter he received. It said that as he contributes nothing, he should do everyone a favor and take his own life. This is not the first such letter he's received but they are interrupted when Peverell employees discover the body of Sonya Clements in the firm's archives room.