Mutation (Cryptid Hunters #4)

Marty O'Hara and his friends Luther Smyth and Dylan Hickock have managed to rescue Marty's cousin, Grace, from the clutches of her grandfather, the nefarious pseudo-naturalist Noah Blackwood. Now their most dangerous mission lies ahead of them. Marty's parents have been missing in Brazil for months, and their trail has all but run cold. With time running out, Marty, Grace, and the Cryptos Island crew race down to Brazil, to the jaguar preserve run by Dr. Robert Lansa and his son, Jake. But even the preserve isn't safe. When their friends begin disappearing one by one, Marty and Grace head into the rain forest in pursuit, where they discover that Noah Blackwood has twisted the natural order of things beyond their wildest, most terrifying dreams.