For the Time Being: A Science Fiction Fantasy [Book]

Twelve graduate-level, Mensa-gifted misfits, or the "Pubbers", set out one night on an adventure to explore a set of steam tunnels beneath their school. Hoping to return home, the group secretly begins to build a time machine. Their scheme is discovered and the Pubbers learn why they were kidnapped in the first place: they'd already promised the aliens 500 years ago that they would build a time machine to save their race from extinction!