"I'm sorry, I can't... I'm broken,"
"Is that what they told you?"
The Doctor skidded to a halt in yet another room in the complex. There, a vaguely cylindrical robot went in a circuitous path, repeatedly fixing things that, ultimately, caused everything to return to its original state.
"Sysiphus," he muttered.
Holly stopped, too, almost blundering into him. She took in the scene and said, "Excuse me?"
The robot paused. "I cannot aid you. I am... broken. I must... fix." And then it trundled on with its endless tasks.
The Doctor, being the Doctor, started fiddling about with paperclips and string. Rigging something up in the circuit where the robot had just been.
Holly followed the poor thing. "What are you doing?"
"I fix things, here. I must fix things here. It is all I am."
This was obviously a combination of someone's cruel joke, and a sad attempt at a perpetual motion machine.
"But why are you fixing this lot? You're making your own problems."
"It is what I am made for. I must fix."
"But... you can just leave. Nobody'll notice that you're gone."
"I'm sorry, I can't... I'm broken."
"Is that what they told you?" said the Doctor. He watched and waited where he was, until the ball that the last fix should have careened down the ramp and into the next invented problem. "Nonsense, of course."
The machine stopped in its tracks. Stared at the sudden equilibrium. "It is... fixed. Now what do I do?"
Holly lead it out of its self-imposed maze. "You can be anything you want to be," she said. "We can help you along, if you like."
"Sure," said the Doctor. "It won't be the first time I had a machine in the TARDIS. Free repairs, a little bit of extra programming. No more endless loops."
"Freedom," added Holly. "And a bit of adventure."
"And I am not broken?" the robot seemed to be having trouble with this concept.
"No," cooed the Doctor. "Come on. Let's have an adventure."