"And we'll beat it again," Jack said, trying to sound assured. "I promise you, Doctor. It is done."

He gripped his arm again, a tight hold. He would be there, and he wasn't going to leave him this time.

As the Doctor's head turned, Jack followed his gaze and saw the haze ahead, the cloud growing and moving closer.

Closer and closing in around them.

It wouldn't be a surprise to learn that if there were going to be any way Jack would be trapped, just about the least he would like would be in a confined space underground (well, under water, but there'd be plenty ground on top of him).

"No!" Jack called out, the panic in his voice. "Doctor don't go that way."

He fumbled, trying to open his wrist strap to get them out of there, but he dropped the light pearl and the area grew even darker.