Doctor arrives, he plays Meglos at his own game and tries a little impersonation. The situation becomes so confused that the Gaztaks lose track of which one is which, enabling the Doctor to redirect the super-weapon at Zolfa-Thura before both he and Meglos are detained by the Gaztaks. Meglos abandons the Earthling, leaving a bemused man watching a cactus creature reassert himself in his laboratory. Meglos knows the Doctor has realigned the weapon. However, the creature is unable to stop the Doctor fleeing back to the TARDIS, taking the Earthling with him, and is also unable to persuade Grugger not to fire the weapon. From the TARDIS the Doctor and his friends witness the destruction of Zolfa-Thura, along with the Gaztaks, Meglos, and the Dodecahedron. Caris and Deedrix return to rebuild Tigella, recognising with Zastor and the Deons that old enmities must be put aside and a new society forged. The Doctor and Romana depart and prepare to take the Earthling home, but as they are leaving Romana receives a message from the Time Lords that she must return to Gallifrey. Production Working titles for this story included The Golden Pentangle and The Last Zolfa-Thuran. This is one of only two multi-part stories to feature all credited cast members in every episode, the other being The Edge of Destruction (1964). This story features the only use in Doctor Who of a camera-linking system known as Scene-Sync that allowed the use of non-static shots of characters superimposed onto a miniature set. As the cameras on the actors were moved, the cameras on the miniature set moved the equivalent scaled amount automatically. The exact scale motion was achieved by trial and error, involving minute adjustments to the voltage delivered to the slave camera's motors. Part Four's closing theme was transposed to the lower key of the original theme music. During production of this story, Madame Tussauds in London debuted the "Doctor Who Exhibition". Included were sculptures of both the Fourth Doctor and his Meglos doppelganger. As a result, Tom Baker is the only person to have appeared twice in the wax museum. When writing the 2010 story The Lodger, Gareth Roberts had thought of making it a sequel to Meglos but this sequel idea was ultimately dropped. Cast notes Jacqueline Hill, who played the First Doctor's companion Barbara Wright, makes a guest appearance as Lexa, marking the first time a companion has