The local constable disregards Lynley's instructions in a hostage situation — in which a villain with a shotgun is holding a young girl hostage — and goes, unarmed, to talk to the villain to try and secure the girl's release. What makes this even more heroic is that the villain is the woman he loves and the hostage is the woman's daughter, who earlier accused him of insincerely trying to be her "dad".
Barbara hiding the sleeping pills the perp forced her to take in her cheek, then spitting them out, tracking the perp to where he'd hidden his victim, and cold-cocking him on the head to rescue said kid. This girl is clever.
The last twenty minutes or so of the episode, for both Lynley and Havers. Their rescue of Hadiyyah, Lynley leaping into the water to save her, and Havers managing to turn the boat around and save them both were all epic and made of awesome.
Lynley engaging a suicidal woman in conversation to prevent her jumping off a parapet with the baby she is holding. Made more awesome by the fact that this was in broad daylight in a busy public area, in view of many spectators. No pressure.