The Doctor manœuvred the little boat alongside ladder that ran down one leg of the oil-rig.  A stiff  wind was blowing up a heavy swell.  The Doctor managed to make up the boat's line to the ladder, then helped Jo to scramble across to it.

'I still say you should have taken Mr Robbins' boat back,' Jo called, as she climbed the vertical ladder.

'I will, Jo,' called the Doctor, now beneath her and climbing.  'And you can return his bicycle at the same time, poor man.'

Jo found it heavy going climbing up to the top.  As she ascended, she took care not to look down in case it made her feel dizzy.  She was much relieved when finally she pulled herself up on to the enclosed deck of the oil-rig.  She found herself in a long wide passage that ran the length of one side of the rig.  The metal wall on the outer side had big windows at regular intervals, the glass containing wire mesh to stop them from cracking in a heavy storm.  With the metal deck and metal walls it was like the interior of a ship, except that there was no roll.

The Doctor pulled himself on to the deck.  'It's not what you'd describe as teeming with life,' observed the Doctor, looking up and down the passage.

'Maybe they're not working here today,' said Jo.

'You don't think they just come out here to work, do you?' said the Doctor.  'Men live on these things for weeks at a time.  Let's take a look around.'

They went along the corridor and found that there were more leading off to other parts of the rig, and steps that led up to another deck above.  After fifteen minutes of searching they found a cabin that was, or had been, inhabited.  It was fitted out with bunks, a table and chairs, a small cooking-stove in a corner, and men's clothes were lying around.  On the table was a game of draughts, the players had obviously left in the middle, and half a glass of beer.

'Just like the Marie Celeste,' commented the Doctor.

'What's that?' Jo asked.

'A ship that was once found at sea,' the Doctor explained.  'There was food on the table, and all the other signs of life, but no on on board.  All the passengers and crew had vanished without trace, and were never seen again.'

Jo shivered.  'Couldn't you be a bit more cheerful?'  This rig is huge.  The men could be anywhere.'

'Why didn't they finish their game of draughts before they went off to do whatever they had to do?' said the Doctor.

Jo was beginning to feel uneasy.  'I've no idea,' she snapped.  'Let's just find them, and stop thinking of nasty ideas!'  She glanced out of the porthole set in the wall of the cabin.  'And another thing, Doctor.  It's beginning to get dark.  We ought to get back to the island.'

'There's plenty of time,' said the Doctor.  'Even if we go back in the dark, there must be lights on at the Naval base or at the café - I can just point the boat the shore lights -'

He stopped suddenly as they both heard a loud explosion.  Jo rushed to the porthole and looked dawn.  'Our boat,' she cried.  'Look!'

The Doctor joined Jo at the porthole.  From here they could see straight down into the water a hundred feet below.  A few pieces of broken, charred wood were floating at the bottom of the ladder- all that remained of Mr. Robbins' boat.

'It must have been the petrol tank,' said the Doctor.

'Petrol tanks can't blow up by themselves,' said Jo.  'Do you realise we're stranded here?'

'Not to worry,' said the Doctor.  'There must be a radio on this rig.  I'll send a message back to shore.  But it's a pity about that man's boat.'