Joy and Mark visit Australia to uncover the reproductive secrets of some of the strangest mammals on Earth: the pouch-wearing marsupials. The kangaroo thrives in one of the driest environments on Earth, the Australian Outback, thanks to its extreme baby-making survival strategy. At a remote research station, Mark uses night-imaging cameras to uncover how wild male kangaroos track down fertile females, and in Queensland’s eucalypt forests he explores how tree-dwelling marsupials – koalas – have mastered gravity-defying sex. At a kangaroo sanctuary, Joy follows the action as kangaroos mate in front of her, uses ultrasound to monitor the progress of a kangaroo’s pregnancy, and witnesses the extraordinary sight of a new-born kangaroo feeding from its mother’s teat inside her pouch. In Adelaide, she learns how critically endangered rock wallabies are being saved using foster mothers. The programme finds out why female kangaroos have three vaginas, how male marsupials use sperm plugs to beat the competition, and how new-born babies the size of a paperclip climb heroically into their mother’s pouch.