S4·E9 Freefall

Max Cassidy vanishes after leaving a message on his wife's voicemail, with both Jack and Ann frantic to find him. While investigating, Jack realises that Max was having an affair, and that he's gotten much deeper into a case than he should have following the murder of his partner, Jimmy, a man Max had felt was too green for undercover work. Both Jack and Ann fear the worst as the team tries to hunt down Max.