The Doctor was deeply regretting not taking off his coat. He was really regretting a good bit of diving into this water without any of the equipment he'd planned for. But that was him to a T, wasn't it? Leaping in without thought, causing chaos without care?

He struggled with the weight, but eventually managed to kick towards the rocks. He nodded to Jack, and then followed the light to the rocks. At the bottom, a small hole about the size of a man poked out through, the light bright on the opposite side. He swam towards it, his thin body easily slipping through. A tunnel greeted him, and he pressed himself through.

This was possibly suicidal. What if this cave didn't lead to anywhere? What if there wasn't air? What if he couldn't turn around?

It broke out to a wide, open space of water full of bright, crackling light. Above him, a pocket of air near the surface of the cave awaited.