Citadel (The concluding volume in The Beachhead trilogy)

Seventeen-year-old Will and his four friends escaped from a tropical island fortress then fought for freedom on a monstrous prison ship. Now they reach the mainland and dock their small cruiser in the harbour of a large city, hoping at last to find answers to their origins.At first the city is deserted, but soon drones attack them from above. At night, sicko adults, diseased, angry and hungry, hunt them down relentlessly. Will, Quentin, Fiona, Rose and Kevin are on the run again, knowing that capture can’t be long from coming.When it does - what awaits the teens behind the high walls and barbed wire of the sinister research hospital, in which robots prowl the wards and sicko humans are processed like cattle? And what lies deep inside the mysterious mountain known as the Citadel?