Complex sentence: The Slayer heroically fends off a large-scale attack of vampires, but is burned at the stake afterwards by the very people she saved as her Watcher, a friar, can do nothing but watch.
Split into simpler sentences: The Slayer heroically fends off a large-scale attack of vampires, but is burned at the stake afterwards by the very people she saved. Her Watcher, a friar, can do nothing but watch.