In Australia, Joy and Mark uncover the reproductive secrets of some of the strangest mammals on Earth - the pouch-wearing marsupials. Thanks to their bizarre way of reproducing, kangaroos thrive in one of the most unpredictable, drought-prone environments on Earth - the Australian Outback. In Queensland's eucalyptus forests, he sees how tree-living marsupials - koalas - have mastered gravity-defying sex. At a kangaroo sanctuary, Joy witnesses a tiny newborn's first steps as it crawls to the pouch, and in Adelaide, she learns how endangered rock wallabies are being saved using foster mothers. During a kangaroo dissection, she learns what makes marsupial reproductive anatomy unique.