The Doctor is rummaging through some old trunks on the TARDIS, when Merlin enters. The Doctor looks up.

"What in the world are you looking for, Doctor?"

"Oh, an old keepsake I had laying around..."

Suddenly he reaches into a box and pulls from it a very large sword. It's long, silver, and has a very finely crafted handle.

"What is that for?"

"Well," the Doctor replies, "it's to help get Rose back."

The Time Lord rushes out of the TARDIS. "Merlin, were you able to line up any men?" he asks.

"Yes..."

"Well good, I'll lead them. We have to get Rose back safe--"

Suddenly a voice is heard: "No, Doctor, I'll lead the men into battle."

They turn to see Lancelot in full gear standing before them. "You should be resting," Merlin says. "The Doctor is well-trained to use a sword."

"But can he make his way around Camelot?" asks Lancelot. "I think not. I know this forest like no one else."

"Well then, what are we waiting for?" asks the Doctor.

As they head for the the forest, Merlin can be seen standing back in the distance.

Deep within the heart of the forest live the Scarboroughs, who make homes of the trees and the caves, and can lurk anywhere. Slowly, the Doctor, Lancelot and the men walk along, looking through the trees and anywhere else an ambush might await. Suddenly, one of the men stops the Doctor. Others stop marching as well, and the whole group falls silent. A wind can be heard whispering through the trees, and over it, a barely audible whistling. All at once, the Scarboroughs spring out of nowhere and attack. The men with the Doctor and Lancelot are quickly taken out. They run through the forest with the Scarboroughs in pursuit. Soon they arrive in a large open area, where the Scarboroughs surround them. The Doctor and Lancelot stand back to back, waiting for them to attack. No one makes a move. Suddenly a large cage surrounds them, entrapping them. It rises and begins moving. They have been captured.

"Where are we being taken?" the Doctor wonders. Guess he'll soon find out.

The two are taken to a large structure on the hillside, which turns out to be the top of an enormous door leading into a hidden fortress. They are escorted through the halls of the fortress - all stone walls, no windows, no metal - and into the depths of a dungeon. There are are what appear to be rooms inside. Various sorts of treasures can be seen everywhere. Lancelot remarks that this subterranean structure must have taken either magic or a lot of labor to create. The Doctor thinks to himself: he's seen this handiwork before, but where?

Soon, the cage stops. Two men open a small door and have the Doctor and Lancelot enter. The door is shut and locked behind them.

They are in what appears to be a bedroom. There is a window, which looks out from high above on a large stone courtyard. They are still underground but it's a city. Outside are houses and small inland lakes. The Doctor notes some action in a nearby area which looks to be a training ground, where men are practicing combat. Lancelot joins him over at the window and cannot believe what he sees. "It's a city below ground! Some work was really put into this. But the question again is how?"

A guard enters the room. "You two are to follow me, and don't try anything funny. King Addicus would like to see you."

Following the guard, the Doctor and Lancelot proceed down a long hall and a few flights of stairs to a large banquet hall. There they see a man sitting in a large thronelike chair.

"Welcome, my friends," the man speaks. "I am Addicus, the commander of this little place."

"How did you build such a large city underground?" asks the Doctor, intrigued. "Must have taken massive help."

Lancelot is not pleased to see this man. He's heard of the things he has done to his prisoners before. But were they prisoners? They weren't chained or anything.

Addicus responds to the doctor's question: "Well, my friend, you are interested, are you? Well then, let me show you. Follow me. This way!" He leads the Doctor and Lancelot, with two sword-bearing guards following, into a small lab of sorts where large crystals are seen. "You see, these are old caves. Many years ago my people and I dwelled here. We found deep within here these crystals which we thought were jewels but turned out to be much more than we expected. They could be used to create tunnels and other things. They were known among my people as magic rods, and using them we created paradise."

The Doctor knows now where he has seen this. Many years ago he visited a planet called Caltax Beta, whose settlers used these same crystals to terraform land into habitable living spaces - but the planet's core became unstable and they had to evacuate. The Doctor had tried to lend a hand to save them but couldn't manage it. Pieces of the planet must have been sent through space and burrowed into the Earth as meteorites. But how long had they been here? Oh well, that was a question for another time. Showing more, Addicus explains how they lived. Lancelot wasn't concerned with that, but he was devising a way to escape. Now, the Doctor may have been occupied with all this but his mind hadn't forgotten why they were here, nor Rose of course.

"So, my friends. My men captured you heading through the forest this way. Might I inquire why you were looking for us?"

"Well your men kidnapped someone - a young woman - and your people don't have the best reputation in the land."

"Oh, you mean the young Rose," Addicus says. "She's safe; we were looking for an escaped thief and Rose just happened to look like her. But that's all been taken care of. If you will follow me, she's this way. She's been my honored guest since she's gotten here."

They file into another room down the hall. Inside, Rose is wearing a period dress. Lancelot and the Doctor can hardly believe their eyes. Running over to the Doctor, Rose hugs him. "It's good to see you," she says.

"You too," he answers and Lancelot says it's good to see her safe.

"Now if you don't mind," Lancelot continues, "we'll be on our way. Assuming we aren't prisoners."

"Nonsense," Addicus says. "Stay! You're my guests for the evening feast."

The Doctor and Lancelot look at each other. Something isn't right here.

Later that evening, they are all seated around a large table covered in heaping platters of food. The Doctor and Lancelot aren't eating much. Rose, on the other hand, is eating nicely.

"So Addicus, the stories of your ways aren't true as the people tell?"

"No, not at all," he says.

"What of your prisoners? The ones you torture and such?"

"Nonsense," he says. "Those we capture are certainly prisoners in a sense, but they are brought here and are given a new home, here in this paradise!"

"But they cannot leave," the Doctor prods. "So they are prisoners."

"Yes, well, they're not so much prisoners as they are permanent guests."

"As with us?" the Doctor asks. "We're permanent guests too?"

Addicus says nothing.

The Doctor knows why. If anyone ever got out, the underground city could become a lost paradise.

Shortly after dinner, they are taken back to the room, where the Doctor and Lancelot devise an escape plan. Rose has been taken back to where she was.

"So Doctor, any ideas?" Lancelot asks.

"Yes," he says, "one."

Shortly, the Doctor calls for the guard, who comes to the door. Lancelot hits the guard over the head with a vase and drags him to a corner, picking up his sword. Lancelot and the Doctor make their way to Rose's room, where they find another guard. Once he is subdued, they enter. Rose is again excited to see them. The Doctor notices Rose has cut her arm.

"What happened?" he asks.

"It's nothing. Just got hit on a tree branch when I was taken from the lake. It's not too bad."

Making their way down the hall, they pass a small room. Inside, the Doctor sees his sword. He enters and picks it up. Down the hall, they try to find a way to the surface. They try to remember the way they got in. Almost to the passage leading there, they are met by a band of men fighting. They turn back and look for another way. They enter a room to hide and notice a stash of crystals, which gives the Doctor an idea. Using a crystal, he begins to form openings to tunnel out, but they don't reach the surface, only reroute to other parts of the caves.

They are now standing in a large room which appears to be the central heating and air supply control. A group of men led by Addicus enters.

"Stop! Return to your rooms and no one will be hurt. But there is no escaping."

Lancelot charges, and begins fighting with the men. Addicus races towards the Doctor wielding a sword; the Doctor raises his own sword and parries the blow. Rose attacks the soldiers with whatever pipes and such she can find. Lancelot is holding his own, while the fight between the Doctor and Addicus has taken them up some stairs. Sparks fly as the Doctor's sword matches Addicus' blow for blow. Soon they are over what appears to be the main fan. The swords clash, when suddenly the Doctor swipes low. Addicus loses his footing, and his sword falls over the side and into the central part of the fan, jamming it. The fan begins to overheat. Addicus hangs off the side as the place begins to rumble. The Doctor, realizing it's about to collapse, reaches for Addicus but the railing gives way. He leaps down the stairs, knowing he can't get to Addicus. Instead, he runs to find Rose. With her in hand, he makes for the door. The inhabitants have the same idea, running for the exits with Lancelot not far behind.

Soon they come to what appears to be an elevator. Using his sonic screwdriver, the Doctor is able to get it moving. Shortly they are being lifted. It takes them to the first floor. Not quite out of the woods yet, they proceed to an opening. Falling rubble deals Lancelot a glancing blow. The Doctor rushes over to help. They barely make it through the opening before a large explosion rocks the entrance, rocks and beams filling the doorway. Rose, the Doctor and Lancelot wonder how many made it out okay. And what of Addicus?

The survivors all gather around, free at last.

"So what now?" Rose asks.

"Back to the castle," the Doctor replies, "and help these individuals become accustomed to living above ground."

Several days pass. The underground inhabitants, now living in Camelot, have blended in well with the locals. Lancelot and Rose have grown close, but she knows they must soon leave. Merlin doesn't need the Doctor anymore; he was able with his help to prolong his last life for another fifty or so years.

The Doctor and Rose stand in the court yard, saying their goodbyes. Suddenly Lancelot reaches over and embraces her in a kiss. The Doctor walks by and coughs.

"Time to go," he says.

Rose walks away. Slowly, she and the doctor enter the TARDIS. Wheezing noises are heard as it disappears.

"Where to next?" asks Rose.

"Who knows?"

In Merlin's lab, Lancelot enters. "Will she ever return in that magic box, Merlin?"

"Maybe," he says, "one day."

Walking over to the table, Lancelot lays a scarf on the table. Suddenly a device begins to go off, beeping loudly.

"What's that?"

"It's a DNA scanner," Merlin replies, "set to find certain DNA, but I don't know why it's beeping like that." Walking over, he asks, "what did you do to set it off?"

"I don't know... I laid this down, and it started making that racket."

Merlin picks something up, waves it over the scarf, and it begins to beep faster. "Where you get this?" he asks.

"It's Rose's. She was wearing it earlier."

On the inside, Merlin finds a small speck of blood where her cut has left a stain. "It's impossible," Merlin breathes.

"What's that?"

"According to this, Rose is a Time Lord..."