2. Into the Belly of the Beast

The scientific crew on the Orpheus submarine runs into severe danger in their quest to find rare micro-organisms. One crew member has died, the Orpheus has been intercepted and two of the crew are trapped and running out of air. They have to escape, but can they risk boarding the mysterious vessel which looms above them?

3. Ghosts of the Deep

The Orpheus crew's quest for renewable energy has led them into danger. They're trapped on Volos, a Russian submarine, and its nuclear reactor is dangerously overheating. Whoever shuts it down will be exposed to lethal radiation. Who will draw the short straw? Meanwhile Clem is determined to find out what part the Volos had in his wife's death.

4. Everything Put Together Falls Apart

The Orpheus is mended, and the captain wants the crew to find more of the rare bio-fuel samples before they return to the surface. The Russian captain has other ideas, however, and instructs his men to kill the crew. In their struggle to escape, some are left behind; will they be able to complete their mission?

5. The Last Breath

The Orpheus crew have found rare bio fuels in the ocean depths, but they must find a way of getting it to the surface safely. With the Russian captain of the Volos submarine determined to stop them, will they manage to stabilise the energy source and make it back to the surface?