“And…” the Doctor was saying in his distracted way as he pushed buttons and pulled levers. “Welcome to…” One last button, and Martha felt the TARDIS land. “Cardiff,” the Doctor finished proudly.
“Cardiff?” Martha repeated, her tone disbelieving. “As in… Wales?” It was so… normal.
The Doctor nodded absently. “The city is built over a rift — like the San Andreas Fault in California, only in time and space instead of rock.” While he spoke, he looked over the energy readings. “The rift gives off energy…” An odd reading caught his eye, breaking the rhythm of his speech. “I just… park, open up the engines…” Not just an odd reading. A very odd reading.
“Like a pit stop?” Martha asked.
“Uh, yes, exactly. Shouldn’t take long… rift’s been active lately.” He squinted at the console. “Really active, actually.” He paused, looking worried. “That sort of energy shouldn’t be… could mean… or it could be… Be right back!” he exclaimed suddenly, running out of the console room.
Martha, who had glanced down at the monitor for her first look at Cardiff, called out for him to wait as he sprung away. But he was down a corridor and out of earshot — mentally if not physically — before Martha could tell him that it appeared that the TARDIS had materialized inside a huge, gadget-filled room. She watched as a dark-haired man struggled to zip up a large black backpack while a blonde woman tugged on his sleeve.
“Doctor!” Martha tried again. The couple was now jogging towards the door of the TARDIS. The Doctor’s only response to Martha’s shout was to increase the volume of his continued stream of technobabble, and Martha caught something about voids and ancient energy before her mouth dropped open in shock.
The blonde had pulled out a key.
A TARDIS key.
Martha was openly gaping when the door burst open.