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.Trapped in the office of the suspicious director, how can Cal evade capture and continue his double act with his twin brother, Ryan? As dangers multiply at every turn, at least he knows he can count on SI-6 - or can he?The clock is ticking ...