"Marty and his best friend, Luther, have managed to rescue Marty's cousin Grace from the clutches of the nefarious pseudo-naturalist Noah Blackwood, but 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 and the Cryptos Island crew race off for Brazil--where they discover that Noah Blackwood has twisted the natural order of things...

Traveling to Brazil to locate a rare crystal treasure being guarded by a native tribe in the Amazon jungle, Geronimo Stilton and his friends navigate a treacherous route filled with crocodiles, giant rats and, piranhas.