A gravatronic tractor beam is used to capture the TARDIS, but accidentally locks on to K9 instead of the Doctor, kidnapping the robot. Firandel and Rolgot are behind the botched kidnap, working for the Sontarans. K9 realises their intention to kidnap and kill the Doctor because of the lack of air on his expected arrival and overpowers his "hosts" before the Doctor and the TARDIS arrive in safety to collect him.