I want to write a story that starts as slice-of-life humor (think Daria) that later genre shifts into a SF thriller. Thing is I don't quite know how. For the slice-of-life humor part, the metaplot is around a now-graduated child prodigy (Janet) hiring herself out as a private tutor and her interactions with typical teenagers. I've got my main character planned forwards, backwards, and sideways but I've not much insight into the other characters, Should I plan them out or let them develop over time? For the SF thriller part, where the grenade lands in the nursery and no one can cope but Janet, I've no idea what the wham moment should be. Why would a thriller antagonist be interested in a high school? Lastly, apart what I can scrape away from TV Tropes I know squat about high school, and the site doesn't have a "zany teen situations" section. Any advice (or lists) you have will be appreciated.