After saving the universe twice, freeing a slave race, rescuing three princesses, becoming a lower god on Pantab III and a antichrist on Brandus II, all in one week, the Doctor admitted he needed a rest. He found a quiet, deserted planet on which to land so Jack could roam while he recovered.
Three days later, the Doctor left the Tardis in search of Jack; he didn't have to go far.
Jack sat cross-legged upon a flat rock, overlooking a lush, green valley with a clear pink lake. A closed book balanced on his leg.
"Jack."
"Doctor."
The Doctor stood beside the rock, following Jack's gaze. "What have you been doing?"
"Contemplating."
"Oh?" the Doctor said, turning his attention to Jack, eyebrow raised.
Jack sighed. "Life. The Universe. Everything."
"Been reading Douglas Adams again?"