This weekend at Mountain Bluff Zoo, Katy and Micah are Junior Researchers. The friends are watching the capuchin monkey group. The keeper is worried about one of the monkeys, a male named Milo who has been steadily gaining weight. Perhaps the kids can figure it out by closely observing his behaviour. At first, Katy and Micah are stumped. But as they spend more time with the monkeys, will they solve the mystery? And, can they come up with some creative ideas to help Milo?