"Time to die," the Doctor snarled and reached for Jack's head.
An arc of silver blue suddenly crackled between them and struck the Doctor in the chest.
The force of it threw both of them back, and the last thing Jack saw before darkness descended was the Doctor hitting the wall opposite.
Martha stopped suddenly, causing Gwen to bump into her.
"What's wrong?" she asked.
"Did you see that?" Martha said.
"See what?"
"The flash of lightning."
"Where?" Ianto said, pushing White Coat in front of him.
Martha pointed to her right. "In the distance, just a flash, but I think we should go that way."
"Why?" Gwen said.
Martha turned to Gwen. "I don't know, but it feels like we should."
"It can't do any harm, we not exactly getting anywhere," Ianto said. "Let's try it."
They'd only gone a few metres when the ground, if it was ground, shifted under their feet.
Jack came round with a start as a silver blue thread brightened in his mind. He blinked at the fact that he was no longer in a war destroyed future nor in the grasp of a Time Lord, intent on doing god knows what to him.
It took him a few second to realise that he was in a weird kind of darkness...he must be inside the black cloud...inside the Chaos.
A flash of lightning blue flickered to his right and he looked round and was up in an instant.
Standing a few feet away, rigid as any statue was the Doctor.
He was wreathed in silver blue that flashed and sparked as it made contact with skin.
Jack moved closer, but stopped when the Doctor's eyes fluttered open, only to reveal the blackness of the Chaos.
"What have you done?" it gasped as lightning blue flashed across the black.
"I took the third choice. You wanted this body, now you'll have to fight someone far more dangerous than me for it."
The Chaos looked into itself and saw a glimmer of something on the edges of its own existence. It saw something powerful...something as ancient as itself...something that was angry.
It hissed and returned its attention to the one thing it could do something about. "Harkness, you should have said yes, now your end will be painful and slow."
Jack stepped back as there was a crackle of energy and the silver blue was replaced by the inky black of the Chaos.
"You and your friends are in my domain now," it said and raised a hand.
Seconds later Ianto, Martha, Gwen and a still subdued White Coat appeared, next to a startled Jack.
The Chaos twitched a hand again and they fell to their knees, gasping for air.
"I know you have a link to his machine, you will sever it or they will die," the Chaos hissed.
It was so intent on it purpose that it didn't notice the darkness around it was brightening, taking on a lightning blue hue.
But Jack noticed, saw what the Chaos didn't, saw what was coming and began to laugh, not with amusement but in horror.
The Chaos frowned. "You find this funny, they are dying and you are amused?"
The Chaos then noticed the change inside its world...no, this wasn't possible, nothing was that powerful...except.
It turned and saw what was coming and with a snarl that was part anger and part fear it moved.
Jack watched helplessly as the Doctor hurtled forwards.
At the same time the others fell forward, taking in huge gulps of air.
Jack wanted to look away, but couldn't.
The Chaos collided head on with it and joined battle. It knew what it was fighting...the Time Lord's machine, all the power of the Vortex within it...the wolf within.
It grabbed hold of the snapping jaws and twisted, its aim to get the wolf on its back.
For a moment the eyes of the wolf and the eyes of Chaos met and there was a moment of stalemate...but only a moment.
The wolf growled a growl that seemed to come from deep within and it sounded like thunder rolling across distant plains.
The Chaos could feel the wolf's jaw tense and it felt it grip on them falter.
With a savage snarl the wolf broke the Chaos's hold on its jaws and whipped its head round, and sank teeth into flesh.
The Chaos screeched as it felt the burn of unlimited power and with an answering growl hammered its fist against the skull of the wolf.
The wolf let out a yelp and teeth tore away from flesh as it reeled from the blows to it head and yelped again as the Chaos heaved it away and it skidded along dark ground.
Jack had flinched as he saw the wolf...that impossible wolf sink its teeth into the Doctor's side and flinched again as flesh was ripped from his body as the wolf was thrown.
He wanted to stop it, but knew that he couldn't, knew this would have only one end...death for one of the protagonists.
The Chaos staggered back, dazed from the shock of the attack by the wolf. It knew it had to win this fight and win it soon, or it would have nothing to use as a host. It looked down at the ragged wound in its hosts side, saw the free flowing blood and exposed nerve and muscle.
A snarl focused its attention on the wolf once more. It gathered all the strength its host had left and with a snarl lunged for the wolf.
As they met in a clash of fur and flesh, sparks of blue mixed with black fizzled and crackled around them and soon Jack couldn't see the two for the sparks.
Deep inside the Doctor's mind a crack appeared in the darkness that was choking it and a small glimmer of gold began to show and began growing.
The Chaos felt it first, felt the searing heat of gold flashing through its consciousness, felt it overwhelming its dark self.
The wolf felt it next, but ignored it and pressed its attack.
The glimmer of gold suddenly became a flash of golden fire and the world around the struggling pair became incandescent.
The Chaos let out a screech of agony as the golden light seared through the black of its world and it thought it heard a voice that sounded like the howling of a storm.
The wolf yowled as it felt the golden light scorch its fur and it cowered at the voice that sound like the one that had mastery over it.
Jack had been watching the static and blinked when it began to change from the blues and blacks of the two combatants to a golden ball of fire and something else...and instinctively he knew he had to look away.
"Don't look!" he managed to yell at the others before his world turned brighter than the sun and he swore he heard a voice and then he heard no more
"Enough!" it howled.
Martha was the first to come round and was startled to find green grass under her face, not the darkness of the Chaos.
She sat up and she saw in front of her what looked like the dome of an observatory, they were back on Earth.
She looked round and saw Ianto and Gwen, but was not surprised when she didn't White Coat, just like a rat she thought.
She looked the other way and saw Jack, lying a few feet away and beginning to stir.
Then she saw beyond that and she paled. "No!
She was up and shaking Jack in seconds, who came round quickly.
"Wha...Martha?" he said slowly.
"Jack," she said and pointed.
Jack turned and he stopped breathing.
Not waiting for the others to come round, they dashed down the hill to what was a deep crater in the ground.
In the centre was the TARDIS, but it wasn't its normal faded blue, it was charred and scorched and smoke was billowing from the open doors.
But it wasn't the TARDIS that drew their attention; it was the figure lying a few feet away.
"Doctor!" Jack yelled and dashed over, expecting him to move and wonder what all the fuss was about.
But there was no movement, and as Jack slid to a halt, the smell of burnt flesh filled his nostril.
"No, please!" he cried and gently turned the Doctor over and was almost sick and he heard Martha make a noise behind him.
One half of the Doctor's face was burnt, the skin blackened and red raw flesh was showing through destroyed skin. The un-burnt part of his face was bloody and a half burnt, half open hole in his side was weeping blood and fluid.
"What have you done?" Jack whispered and he nearly dropped the Doctor when he opened his eyes.
"Doctor," Jack said, relieved that he was still alive.
But the Doctor didn't seem to know he was there. He was mumbling something and Jack moved closer to hear what he was saying and what he heard made his blood chill.
"Darkness, nothing but darkness, nothing but shades of darkness."
TBC in Shades of Darkness.