The Enemy Within (Part 6) - S5.E6

Alisha obtains evidence to incriminate Drummond from his wife Chrissy and, after she is attacked and it is stolen, its recovery proves that Drummond's son Luke was the attacker. Realizing that the game could be up for him Drummond goes to see Joseph and asks him to keep a secret. The connection between Joseph, Mo Jones and Drummond will eventually solve the mystery as to who killed Sarah, and Martha and her husband and bring Drummond down.