While in the seaside English city of Brighton, Spike chooses the wrong prey. That one bad choice leads to a vasty different season two, with Spike in Sunnydale, willing to team up with Buffy on a quest for revenge.
Please keep in mind that this is set during season two, before the addition of Dawn memories made Joyce a better mother. In season one she was actively reading parenting books like she'd never actually done it before, and it was stated that her characterization from the movie was canon.