Complex sentence: She leaves as the Hong-Kong watcher tracks her to finally kill her, however at the last moment the "Wiper" appears (the same who helped Nick remove his memory) and erases her memory, thereby saving Cassie.
Split into simpler sentences: She leaves as the Hong Kong watcher tracks her to finally kill her. However, at the last moment, the Wiper appears (the same who helped Nick remove his memory) and erases her memory, thereby saving Cassie.