The famous faces discover their final mission will be to swim with 18-foot tiger sharks. Ade Adepitan struggles to master his special diving equipment during a training exercise and makes a mad dash for a boat with sharks all around him. Meanwhile, Lucy Punch and Ross Noble find themselves in 'predator alley', Helen George suffers a panic attack and falls behind the team during scuba training, and the stars enjoy a spectacular coral reef dive before learning about their next encounter