Doctor Who (William Hartnell) and his companions land in a strange alien world among the Menoptra, the planet's friendly residents. But the Doctor soon discovers the planet is ensnared in an evil web crafted by the mysterious Zarbi species. The web not only prevents the Doctor from leaving, it's also slowly destroying the Menoptra. Will the Doctor and his newfound allies find the Zarbi's weakness and exploit it in time to save the planet?