Through flashbacks, we see much of Angel's history. We see him sired by Darla in 1753, driving Drusilla mad and then siring her in 1860, and being cursed with a soul by the Kalderash clan in 1898. We then see his descent into madness until he is saved by the demon Whistler in 1996 that shows him the one thing that can save him and give his life meaning.
In the present, Angelus hatches a plan to awaken the demon Acathla, who will open a gateway to a hell dimension, and bring Hell to Earth.
Buffy and Willow discover Jenny's plan to restore Angel's soul, and Willow begins to work on recreating the spell. Buffy readies herself to stop Angel, and Kendra arrives with a powerful new weapon - a sword that can kill Acathla, who's just come in time to re-open hell.