Zoe, Lassie and Harvey are with Graham in a nearby town when Sarah calls them with an emergency. Mrs. Lee has been bitten by a poisonous spider and needs antivenin. Rushing home, Graham and the kids encounter a couple of tourists who have got themselves into trouble. Graham is duty-bound to remain behind. Now it's up to Lassie, Zoe and Harvey to find the quickest way into the valley... and that means rafting down the notoriously dangerous rapids.