Episode 9 of "Angel"
s01e09 Hero

Angel tells Doyle of his human experience, and meeting the Powers that Be, but Doyle doesn't have much time to react because work beckons. They soon find a group of half-breed demons and learn the demon racist group, The Scourge, are in town and out for blood. They conspire to rescue the half-demons: Angel goes undercover for the Scourge, and Cordelia and Doyle arrange the half-demons' safe passage to an island. When one of the half demons runs away, Doyle follows him and this delays the departure. While Doyle is away, Cordelia learns of his true identity. Meanwhile, on the inside, Angel learns the strategy to eliminate the half-demon breed population: The Scourge have built a machine whose rays can wipe out any human within a 1/4 mile radius. Angel soon escapes the Scourge and goes to the ship to warn Doyle and Cordelia. He is followed by the soldiers, who place the deadly machine on the ship. With the lives of dozens in jeopardy, Angel and Doyle realize that one of them will have to die in order to disconnect the beams. Though Angel protests, Doyle decides to make the sacrifice. He engages Cordelia in a passionate embrace, then meets the machine. He successfully disconnects it, then dies.