Sean Fletcher and Anita Rani explore the rugged hills and valleys of west Exmoor, where landscape-scale change is occurring with the introduction of large animals to aid nature restoration. Sean meets some unusual ecosystem engineers - a herd of water buffalo, set to be released to create wetland habitats. He also helps round up 23 Exmoor ponies ready for their annual health check. Anita witnesses hairy Mangalitsa pigs unwittingly creating the perfect environment for the rare high brown fritillary butterfly. We also learn the significance of the west Exmoor landscape to mathematician and writer Ada Lovelace and catch up with the ranger team determined to keep deer out of their woodlands. Over in the Cotswolds, the weather is still hampering Adam Henson's harvest, but his youngest lambs are finally fit for market.