When Harriet Bailey's young cousins discover an unusual lizard wandering around Cobble Hill Farm, she is stunned to learn that the reptile is not only endangered, but originates from the Caribbean. So how did it end up in White Church Bay? Exotic-animal veterinarian Dr. Jason Peel and private Zoo owner Victoria Langford tells her that animal smuggling is a big problem in Britain and that their new lizard friend, Mango, may be the latest case. When more non-native creatures begin to pop up left and right, Harriet has to wonder if someone in White Church Bay is behind it all.

Meanwhile, Victoria's long-lost brother, Nick, arrives at Moorland Zoo. Twenty years ago, Nick vanished in a boating accident and was presumed dead. Now he claims he wants to explain his absence and reconnect with his family, but the timing is certainly suspicious. Is there an ulterior motive behind Nick's reappearance?