M is for... Megara

Justice Machines, programmed to follow the letter of the law without deviation, encountered by the Fourth Doctor. In Earth's prehistory two of them had been escorting the criminal Cesair of Diplos to trial when their spacecraft became stranded in hyperspace. The Megara, seemingly insubstantial beings which appeared as floating flashing lights, remained locked in their quarters for centuries until unwittingly freed by the Doctor. Cesair, in the meantime, had made it to Earth where she had established a power base in the south west of England. 

Breaking the seal on their door turned out to be crime, punishable by death, and the Doctor found himself on trial. The Megara failed to prosecute Cesair as they did not recognise her in her new human guise. The Doctor had to trick them into discovering her true identity when they tried to execute him, by dragging her into their attack. They then used their mind probes to ascertain if she was unharmed - thus learning who she really was. They transported her to a Neoloithic stone circle where she was turned to stone herself for her many crimes. She had possessed the third segment of the Key to Time, and the Doctor used this to transport the machines to the other side of the universe before they could complete their action against him.

However, the machines are relentless, and will never stop until they have completed their work, so the Megara are still out there in the universe, seeking the criminal Doctor...

Voiced by: Gerald Cross, David McAlister. Appearances: The Stones of Blood (1978).

• The Megara were envisaged as metal spheres by their creator, David Fisher, but the production team were concerned they might be accused of copying the Imperial interrogation 'droid from Star Wars. They were realised instead by puppeteers using lights on the end of rods, filmed against a black backdrop.
• Gerald Cross voiced the White Guardian at the beginning of the story, to save getting Cyril Luckham back for such a small role.
• Megara is an ancient town in Greece, in the Isthmus of Corinth. It was also the name of the wife of the mythical hero Heracles.