Angel joins Doyle's crusade to save a group of peaceful demons from The Scourge, a storm trooper-esque army of pure blood demons that persecute mixed blood demons. The events lead all groups to a climatic showdown aboard a freighter where Doyle finally reveals the real reason why he was sent to Angel, confesses his true demon/human identity to Cordelia, and makes the ultimate sacrifice for his friends in saving the group by deactivating a bomb sent by the Scourge to kill everyone.
Quotes and trivia
Doyle: (To Angel, just before punching him off the platform so that he, not Angel, could sacrifice himself and stop the Scourge) A good fight, yeah? You never know until you've been tested. I get that now.
Doyle: (After kissing Cordelia and just before he leaps onto the Scourge bomb and sacrifices himself) Too bad we'll never know... (Turns demon face)... if this is a face you could learn to love.
Doyle: (In the commercial seen in the end): Is that it? Am I done?
Hero on Wikipedia