With the park up and running, Nigel leaves Bob and Suzanne to tend to the new arrivals and heads on his next adventure — back 10,000 years to the Ice Age, in search of the last remaining woolly mammoths.

After an unexpected encounter with a cave bear, he finds an injured female mammoth pining for her dead sister, killed by hunters. Too weak to even stand, Nigel keeps watch overnight. The next day, when she is stronger, he lures her through the portal and back to the safety of the park.

The team decides to call her Martha. Unfortunately Martha won't eat anything, even though she is making a good recovery, has settled into her new enclosure well and the team are attempting to feed her fresh hay on a daily basis. It's a mystery.

Nigel heads back to the Ice Age once again, this time to the mammoth heyday, in the hope that he can find something that will tempt her. Nigel doesn't just manage to bring back some Ice Age grass, he also comes back with an Elasmotherium — a giant woolly rhinoceros with a six-foot horn.

Despite Nigel's attempts, Martha still won't eat. Veterinarian Suzanne discovers the real reason Martha has no appetite, leading the team to risk an extraordinary experiment.