We last left Susan in Mike's house with Zach holding her hostage at gunpoint. He's waiting to kill Mike because he thinks he killed his father, Paul. When Mike comes home, Susan tackles Zach. In the resulting confusion, Susan trips and falls, the gun goes off harmlessly and Zach runs off.
At the hospital, where Susan is being treated for the lip she accidentally bit, Julie hears Mike giving police a different version of events, one that downplays Zach's murderous intentions.