Deenie, Gabby and Lise are best friends – a tight girl-unit negotiating their way through the troubled waters of their teens, a world of sex, secrets and intense relationships. When first Lise then Gabby falls prey to a mysterious illness, hysteria sweeps their school and, as more girls succumb, Deenie finds herself an outsider, baffled by the terrifying illness and scared that it could all be because of something she has done.