Tycho must master his fears, and those of his fellow Overbridge dwellers, to cross Blackwater bridge and attempt to rescue his sister, Sophie - the Lightmaker - from the evil Ink-u-bi who, because they are afraid of light, have stolen it - and Sophie - from the village. Early in his quest - in fact, before he sets foot on the brige - he's so overwhelmed by the horrors before him, that he is just about to turn back when, one-by-one, some of the other Overbridgers join him on his mission.