Fly into a Rage, Make a Bad Landing

S5 E21: When Detective Bell's girlfriend, Chantal (Chasten Harmon), is assaulted and her ex-husband is killed soon after, in what Holmes and Watson discover is a staged suicide, they search for one suspect behind the linked crimes. Also, as Bell fights the urge to seek his own brand of justice for Chantal, Sherlock makes a heartbreaking realization about the detective's past.