Tides of Time

Alternate BtVS S6/AtS S3: Buffy is killed during an apocalyptic battle, and Angel is forced to wander the devastated earth alone. 100 years into the future he is sent back in time by the PTB to ensure Buffy isn't killed, and history doesn't repeat itself. Can he prevent Buffy's death, or will their complicated relationship get in the way? Angel's P.O.V.