Note: This is for the logicians. In particular note the sections that have been highlighted below in Bold-Italics.

Ch 11: The Guardians of Horus - from “Dr Who and The Pyramids of Mars”

There came a sudden scream from Sarah, just as suddenly cut off by a hollow, ringing sound. The Doctor whirled round. Sarah was trapped inside a transparent glass bell. She hammered frantically at the glass, her lips moving soundlessly.

The Doctor moved round the bell, studying it. ‘A Decatron crucible,’ he muttered to himself. There was no way to break into it—it would have to be removed by the agency which had placed it there. Unless it was removed, and quickly, Sarah was going to die of suffocation. ‘All right, Sarah, keep calm,’ called the Doctor, although he knew she couldn’t hear him.

Inside the bell, Sarah was shouting frantically. The Doctor sighed. ‘Oh, Sarah, I should never have brought you here.’ Then he lip-read her words.

‘Look out. Behind you.’.

The Doctor spun round. Two Mummies had materialised in the darkness. They were similar to the robot Servants of Sutekh, but larger, and the golden ornamentation of their bindings seemed to suggest some kind of rank.

A voice spoke out of the darkness. It was like and yet unlike that of Sutekh, its tones holding wisdom and power rather than Sutekh’s cruelty and hatred. ‘Intruders,’ the great voice boomed, ‘you face the twin guardians of Horus. One is programmed to deceive, the other points truly. These two switches control your fate—instant freedom, or instant death.’

A section of wall with two switches set into it was suddenly illuminated.

The Doctor walked over to the switches and stood before them.

The voice said, ‘Before you choose you can ask one guardian one question. This is the riddle of the Osirians. Which is the guardian of life?’

The Doctor’s mind was racing frantically. He glanced across at Sarah, already showing signs of distress inside the glass bell. Unless he solved the riddle soon she was doomed. He looked again at the two impassive figures of the Mummies. ‘Which indeed,’ he thought. ‘Now if they’re contra-programmed, so one must always give a false indication ...’

The Doctor smiled. He turned to the nearest guardian. ‘One question, eh? Now, if I were to ask your chum there, your fellow guardian, which was the switch that meant life—which one would he indicate?’

The guardian swung round and pointed to the switch on the Doctor’s right. The Doctor nodded. ‘I see. So if you’re the true guardian, that must be the death switch. And if you’re the automatic liar, you’re trying to deceive me. So that must still be the death switch.’ Hoping his logic was water-tight, the Doctor pulled the switch on his left. The two guardians disappeared—and so did the glass bell surrounding Sarah. Gasping for breath she staggered out into the Doctor’s arms. He steadied her on her feet. ‘Are you all right?’ She nodded weakly. ‘Then come on. We’ve got no time to lose.’