The TARDIS lands on the jungle planet Deva Loka, where an Earth expedition has been sent to study the Kinda, a tribe of primitive people. Three team members have already vanished. Are the Kinda as primitive as they seem?

Sanders meets Panna and Karuna who leave a lasting impression on him, while the Dukkha does the same on Tegan. When Hindle's breakdown begins, the Doctor and Todd are in danger.

Aris now carries the mark of the Mara and has gained voice, so Panna shows the Doctor and Todd exactly what the past, present and future hold for Deva Loka.

As the Mara finally breaks free of its dream dimension, the Kinda must do everything they can to contain it. Hindle's need to destroy everything and everyone is unstoppable.

Tegan steers the TARDIS to the planet Manussa, without meaning to - but why? And is it a coincidence that the planet is about to celebrate the 500th anniversary of the expulsion of the insidious Mara?

The Doctor talks to Ambril and Chela to try and stop the 500th anniversary celebrations. A possessed Tegan finds herself in Dugdale's Hall of Mirrors to where she summons Lon. The Doctor and Nyssa return to the caves.

The possessed Tegan and Lon try to find the whereabouts of the Great Crystal. The Doctor finds himself in prison, with only Nyssa to try and get him out. Chela tells the Doctor tales of Dojjen.

The Doctor and the original snakedancer Dojjen work to rid the planet of the Mara.