Cal is undercover on Shadow Island, investigating the secrets hidden beneath the surface of this tropical paradise. Evading search parties, planning rescue missions and sneaking through a maze of hidden tunnels is now an average day for Cal.Ryan has disappeared and Cal's suspicions are raised when he receives a cryptic message: 90 days. Cal agrees to work as an undercover agent for SI-6 to discover the whereabouts of his twin. But at an island getaway for troubled teens, Cal has to face his most heart-stopping challenges yet. He has 90 days.The clock is ticking.