Zoe, Harvey, Graham, Beth and Lassie are forced to interrupt their hike on the valley glacier when they notice that its peak is in danger of collapsing. Beth seems hugely upset at the idea. Later, when Lassie notices Beth's car parked at the foot of the glacier, Harvey realizes that his mother has been hiding something from him. Despite the danger, he sets out to look for her with Zoe and Lassie.