Long Day's Journey
A combination of Wesley's research and a tip-off from Gwen lead the Angel Investigations gang to realise that the Beast is killing a group of ancient totems, the Ra-Tet, and removing some element from each of them.
Angel and Gwen go in search of one of the only two that remain alive. They're too late for one, but an overweight man appears and reveals that he, Manjet, is the last. The Beast, he says, is planning to blot out the sun with the relics he's removing from the Ra-Tet.
The gang guard him at Gwen's palatial home, but somehow he still meets his end. With only one option, they go after the Beast himself, but fail once again.
As the sun begins to dim, the Beast mentions a meeting between Angelus and himself, which Angel cannot remember. Wesley realises that Angelus' memories are the key to destroying the Beast.