It took all the Doctor's strength to pull Jo away.  She fought him desperately, and although she was unable to escape, her struggles prevented the Doctor from dealing with the box.  By now it was glowing white hot, and giving out clouds of choking smoke.

The laboratory door opened and the Brigadier  and Captain Yates entered.  To their amazement they saw Jo and the Doctor fighting fiercely.

At the sight of them, the Doctor lifted Jo off her feet, and literally threw her across the room.  'Hold her!' he yelled.  Jo cannoned into the two soldiers like a well aimed ball in a skittle alley.  All three collapsed in a tangle of arms and legs.

The Doctor whipped of his jacket and wrapped it round the box.  Immediately the jacket started to burn.  The Doctor ran to the window and hurled the blazing bundle through the glass.  There was a shattering crash, a splash, then a tremendous 'whumph'.  The Doctor saw a tremendous waterspout surge up from the little canal.  There were clouds of steam, and the murky water hissed and bubbled.

The dishevelled Brigadier, who had managed to untangle himself from Jo and Yates, came and stood beside the Doctor, looking down at the seething canal.  'There'll be complaints about that, you know,' he said disapprovingly.

The Doctor looked at him with grim amusement.  'My dear Lethbridge-Stewart, if I hadn't got rid of that box, none of us would have been here to listen to them.'

'Suppose you're right,' said the Brigadier philosophically.  'What was that thing?'

'Saturnian solar bomb.  Produces intense, localised heat.  It would have charred everything and everyone in this room into a heap of fine white ash.'

The Brigadier shuddered.  'How the blazes did it get past the security checks?'

'I'm afraid Jo brought it in.'

'Nonsense.  Miss Grant would never...'

'Look at her!' interrupted the Doctor.  The Brigadier turned.  Jo was standing quietly beside Yates, her eyes vacantly staring into space.

'Miss Grant,' snapped the Brigadier.  Jo didn't move.

'She can't hear you,' said the Doctor gently.  'She's in a state of post-hypnotic shock.'

'Hypnotised?' repeated the Brigadier incredulously.  'Who did it?'

'The Master, of course.  Why else do you think she tried to send us all up in smoke?'  The Doctor crossed to Jo, and pushed her gently into a chair.  Jo gazed ahead unseeing, as the Doctor peered into her eyes and took her pulse.

Captain Yates said, 'Look here, Doctor, I thought no hypnotist could make anyone do anything they didn't want to?'

'Not the average hypnotist, perhaps.  But the Master can manipulate the human mind as he pleases.'