Sid is soon rescued by Manny, a gruff woolly mammoth heading north, who fights the rhinos off and continues on his path. Sid joins Manny, not wanting to be alone and unprotected. Manny is annoyed by Sid's outgoing demeanor and wishes to migrate on his own, but Sid nonetheless continues to follow Manny. Meanwhile, Soto, the leader of a "Smilodon" pack, wants revenge on a neanderthal tribe for killing half of his pack by eating the chief's infant son, Roshan, alive. Soto leads a raid on the neanderthal camp, during which Roshan's mother is separated from everyone else and jumps down a waterfall upon being cornered by Soto's lieutenant, Diego. As punishment for his failure to retrieve Roshan, Diego is sent to find and retrieve the him while the rest of the pack waits for him at a mountain known as Half-Peak. Later, Sid and Manny encounter the mother struggling out of the lake, dying from her plunge. The mother only has enough strength to entrust Roshan to Manny before she dies and disappears into the water. After much persuasion by Sid, they decide to return the baby, but when they reach the neanderthal settlement, they find it deserted. They meet up with Diego, who convinces the pair to let him help by tracking the neanderthals. The four travel on, with Diego secretly leading them to Half-Peak where his pack is waiting to ambush them. After encountering several misadventures on their way, the group reaches a cave with several cave paintings. There, Sid and Diego learn about Manny's past and his previous interactions with the neanderthal hunters, in which they slaughtered his family, consisting of his mate and child, leaving Manny a depressed loner. Later, the group almost reaches their destination, Half-Peak, only to encounter a forming river of lava. Manny and Sid, along with Roshan, make it across safely, but Diego ends up hanging on a cliff, about to fall into the lava. Manny saves him, narrowly missing certain death by falling into the lava himself. The herd takes a break for the night, and Roshan takes his first walking steps towards Diego, who starts to have a change of heart about his mission. The next day, the herd approaches the ambush, causing Diego, now full of respect for Manny for saving his life to change his mind and confess to Manny and Sid about the ambush. As the pair turn hostile towards him, Diego asks for their trust and tries to foil the attack.