Ellen smiled at Bosley at the Cheerio restaurant, and he wanted to stay with her instead of getting started on the three days worth of paperwork waiting for the team back at the office. This led him to rant about how he rarely got to work in the field and challenge the Angels to a game of hide and seek.
Ellen went on a date with Bosley, drugged him, kidnapped him, stole his gun, and took him to a secluded place where Lawrence tried to kill him. The Angels stopped this from happening and captured Ellen and Lawrence.