While Billy was practising in an empty school gym, Katie and Devon were watching him and discussing his progress. When Devon started complimenting Billy, Katie figured he had a crush on Billy.
Later that night Devon and Billy went to an abandoned store where zompires had been spotted. While they were staking out the place a zompire appeared. Devon staked it and he told Billy, as his Watcher, that he was not yet ready to fight.
Later yet back at Billy's home they continued the discussion when on TV a news report came on saying that zompires had overrun a public library and were holding hostages there. Billy's grandmother volunteered there and so Billy wanted to go there. Devon told him he could not, not yet, but Billy ignored him.
The police had blocked off the entrance to the library, but having grown up around it, Billy knew a secret way to get in. Devon had come after him though and he admitted to liking Billy and having set up the Slayer/watcher thing in an attempt to get closer. He knew though that Billy still wanted to go save his grandmother and so Devon decided to join him. And so together they snuck into the library. They continued on unnoticed because Billy knew the way, but when one bumped into him the whole group was alerted to them. They quickly ran away to regroup and before charging the zompires, Billy kissed Devon. While Billy starting slaying zompires, Devon sought out the survivors. Together they dispatched of the zompires and saved the captives including Billy's grandmother.
Devon - "At some point, you have to come up with a new way of dealing with these exercises. I'm running out of speed bags."
Billy - "And I'm running out of knives. We all make sacrifices."
Billy - "We're here, we know they're amassing numbers, likely in preparation for some kind of event which will probably not be good ... and now there's smiling. Why is there smiling? Is this a nervous laughter-in-the-face-of-danger thing, or--"
Devon - "I'm smiling because I'm impressed by your moxie."
Devon - "I didn't mean you can't beat them. I meant you can't beat them yet. Not without a plan--"
Billy - "Screw your plan. And screw you. She's the only person in the world who cares about me, loves me for who I am. She stood by me when no one else was there. No one. I'm saving her. With or without you."
Devon - "I didn't expect laughter. I can't lie. This is disconcerting."
Billy - "You ... I'm sorry. You ... like me? You're the coolest guy in school ..."
Devon - "Well, yeah. So what? You're the smartest guy in school. I have a thing for nerds."
Devon - "And after we crawl through tunnels, break into a hostage situation, fight zompires, save your grandmother, and don't get killed ... then we can talk about what we mean to each other."