Facing continued threats from the "Acrocanthosaurus", Red, her sister and the chicks are forced up into the mountains. They encounter ice and snow for the first time, and kill a segnosaur in a cave, turning the den into their nest. The older chick accompanies the two adults on hunting expeditions. One day the raptors encounter a strange creature they have never seen—a whip-tailed diplodocid who inflicts wounds on Red and her sister; the older chick is forced to set off alone and find the pack's food. This calamity coincides with the arrival of a large pack of smaller raptors known as "Deinonychus". They surround the nest and wait for the wounded raptors to become weak enough to attack.