In an attempt to lighten the Doctor's mood, his companion Bernice suggests an investigation of a planetary system of seven planets that had seemingly vanished. The TARDIS materializes on the worst of the seven and the two are assailed by multiple types of threats.
Bernice suggests investigating a planetary system with seven planets that vanished for the purpose of lifting the Doctor's spirits. The TARDIS lands on the most perilous planet, where they encounter multiple kinds of threats.