Angel (1999) - 4x10 - Awakening

Cordelia reveals that The Beast and Angelus used to be a team.
She had a vision which let her sample the past of Angel's alter-ego. Wesley arrives at the hotel, he brings a Shaman with him named Wo-Pang. He has the ability to extract and replace souls. After much discussion, the gang decide that the only way to find information on The Beast is to ask his 'partner in crime'. Wo-Pang sedates Angel and inserts a simulation into his mind where everyone is happy and The Beast is dead, Angel and Cordelia make love and Angel wakes up in reality, minus one soul.