Time is a complex thing, twisting and bending into impossible things. One man once said, "People assume that time is a strict progression of cause to effect, but from a non-linear, non-subjective viewpoint - it's more like a big ball of wibbly wobbly... timey wimey... stuff."
But time has to have a means for people to travel it right? That's where the Time Vortex comes in. What is the Time Vortex? That same man mentioned that, "Just as people didn't "exist" in the TARDIS, travel through the Vortex took "no time" and was actually "outside" of time and space meaning the Vortex itself was "nowhere."
And that man is known to travel through time in a Blue Police Box called the TARDIS. This man also often brings along a companion. This man is the Doctor. And he doesn't exactly know how to pilot this time machine.
A sound only familiar to those who know who comes with it sings throughout the air in London. A Blue Box begins to appear, invisible to those who haven't met the Doctor. As the TARDIS sounds it's bell that it has landed, the blue door open and out comes the man himself, The Doctor. "Just going to pop off and get some tea!"
He shouts over his shoulder to back to who ever was inside the TARDIS.
The head of a girl appears by the door, shouting after The Doctor. "Make sure you bring ours back this time!"
She shouted before disappearing back inside the TARDIS, closing the doors behind her.
As the Doctor went off to get himself some tea, another man with a TARDIS appears not far off. This man commonly know as Theta. He too, off to get himself so tea, finds himself in the path of said Doctor. But when they return to The Doctor's TARDIS, chatting about who knows what, the TARDIS suddenly begins to malfunction and dematerializes into the Time Vortex.
In a flurry of fright and flight, the Doctor and Theta set off to Theta's TARDIS to retrieve the missing TARDIS and companions, but, sadly, The Doctor's type 40 TARDIS somehow caused the type 57 to malfunction as well, rendering it useless in time travel for the moment.
Meanwhile, inside the high flying TARDIS, said companions fight to get back. But that isn't their only fight, something has begun to leech the TARDIS energy. When the energy runs out, it's game over.
And their only means of help? A phone.