The parallel Inferno has broken through the Earth's crust, unleashing terrible seismic forces and dooming the planet. The Doctor hopes to return and save his world. But the bestial primords are closing in...

Christopher Benjamin, Dave Carter, Derek Newark, Ian Fairbairn, John Levene, Keith James, Nicholas Courtney, Olaf Pooley, Pat Gorman, Peter Thompson, Philip Ryan, Sheila Dunn