Sarah now invites herself into Irongron's kitchen, using the opportunity to drug the food, thereby knocking out Irongron's men. Linx determines his ship is repaired enough to effect a departure. A crazed and half drugged Irongron arrives and accuses Linx of betraying him; the Sontaran responds by killing him and is in turn shot by Hal. Linx falls dead over his controls, triggering the launch mechanism. Knowing the place is about to explode when the shuttle takes off, Hal awakes Bloodaxe, who rouses the remaining men and tells them to flee, while the Doctor hurries the last of his allies out of the castle. It explodes moments before the Doctor and Sarah depart in the TARDIS. Production Working titles for this story included The Time Fugitive and The Time Survivor. The original outline for the serial was humorously submitted to the production office in the form of a "Field report from Sontaran Field Marshal Hol Mes, to Terran Cedicks". Location shooting of both Wessex Castle and Irongron's castle was done at Peckforton Castle, in Cheshire, utilising different views. The serial also stars Kevin Lindsay as Commander Linx. Lindsay reappeared as Cho-je in Jon Pertwee's last episode, Planet of the Spiders, and again as two Sontarans in Tom Baker's third story The Sontaran Experiment. The story introduces a new opening sequence that includes a slit-scan "time tunnel" effect. It also introduces a new, diamond-shaped logo. These remained in use until 1980. This is the first story in the series history to refer to each segment as a 'Part' rather than 'Episode'. This remained until the end of the classic series with the exception of Destiny of the Daleks. Broadcast and reception The BBC Audience Research Report taken for the fourth episode was positive, particularly the climax. However, there was a minority that felt it was too far-fetched or slapstick. In The Discontinuity Guide (1995), Paul Cornell, Martin Day, and Keith Topping wrote that the story was "a rather wonderful romp" and "one of Robert Holmes' funniest". David J. Howe and Stephen James Walker in The Television Companion (1998) gave a mixed review, stating that it was "enjoyable", especially in its dialogue and characters, but "lacks the sort of impact ideally needed to launch a new run of adventures". They felt that it was "absurd" for scientists to be under custody by UNIT, that the scientists were "clichéd and unbelievable", and the