A/N: This chapter marks the end of part one. Part two is still being written and beta'd, but it will be with you ASAP.

I hope you're enjoying the story so far. Thanks to everyone who's reviewed and/or favourited. And, as always, big thanks to StillThunder86 for being a great beta.

CHAPTER SEVEN
Choices

Back in the guards' lounge, Joe was jerked from sleep by the persistant beeping of an alarm.

"I told you to shut off that racket, Greaves!" he growled, without opening his eyes.

The alarm continued to blare at him, and Joe finally got up and stumbled over to the control panel himself.

"Greaves? Where are you, ya useless lump?" he called. There was no answer. Then he remembered, the kid had gone to out on patrol. Joe glanced at the clock on the wall. What was taking him so long, he wondered. And why had the alarm stared up again, after Greaves switched it off? Joe cast a look around the cosy lounge, and patted his new holster. If he wanted to keep this job, he'd better go and make sure that everything really was alright, right? Not that anything could get loose around here, not with all the surveillance and security and all, but still, it wouldn't hurt to show a bit of initiative, would it?

Idly he wondered where his junior partner had gotten to, then dismissed the thought. He was glad Greaves wasn't with him – the kid would only end up doing something stupid that would make them both look bad. Joe checked the location of the alarm on the computerised map of the building and saw that a technician had triggered his personal alarm somewhere between holding cells seven and nine. That was close enough to the main entrance to be a cause for concern. Joe wondered if Greaves had accidentally set it while on his own patrol - messing with a PDA that didn't belong to him, or something equally stupid. He smiled at the prospect of getting the idiot fired for good. Joe set off, swinging his night stick and swaggering a little as befitted his smart new uniform.

-TMNT-

The five escaping prisoners made it back to the corner that Mack said lead to the exit. Leo and Don were at the front of the group with Mack walking between them, scenting the way to the exit. Mikey came next, and finally Raph, keeping a watchful eye out for trouble from behind. After a few more turns, Mack stopped beside a box set into the wall, about four feet off the ground. It was an opaque grey and held closed with a padlock.

Mack moved a little distance away from the turtles, and slowly rose into his most human form. He steeled himself mentally. This was the crunch – if the escape failed now, all would be lost. He was trusting these strangers with everything. Part of his mind screamed at him not to be such an idiot, but he ignored it.

"These are the locks, operating the main gate," he said, indicating the box on the wall, and pointing to another exactly like it on the other side of the corridor. Mack made an effort to speak clearly, shaping his face as close to human as he could, though his panther fur still covered his body, and his long tail twitched with the effort of staying balanced on two feet.

"Which of you is the fastest runner?" Mack asked.

Mikey instantly said, "I am!" Raph rolled his eyes but didn't contradict him. Leo and Don nodded.

"Yes, Mikey's the fastest of all of us," Don confirmed. "Why is that important?"

"These locks are meant to be opened by guards," Mack explained. "Once the code is entered, the gates remain open for only a few seconds. Both codes must be entered at the same time. I take one, and... Mikey... does the other. The res' of you, at gate. It open – we run, 'kay?"

Mack's voice had grown more guttural during this speech, which was the second longest he had made since he couldn't remember when. Don watched with mounting interest as Mack's muzzle visibly lengthened, but Raph nodded to show that they'd understood. Moving in his stooped, bipedal form, Mack shuffled over to the box and broke the lock with one swipe of his clawed hand. He indicated the keypad inside.

"3, 7, 2, 5, 1. 'kay?" Mack pointed to each button in turn, careful to avoid pressing any of them. Mikey watched closely.

"3-7-2-5-1, gotcha," the turtle repeated. Mack grunted once and went over to his own box. He saw that Raph was already there, having broken the padlock with one of his sais.

"Ya OK to do this one, Mack? You don't move so fast on two feet," Raph said, quietly.

"Yeah, fine," Mack assured him. "Go four feet to run, go fas'."

"Everyone ready?" That was Leo's voice, calling from beside the gates where he stood with Don. "Raph, get over here!"

As Raphael turned to join his brothers, they were all dazzled by a beam of torchlight. A uniformed guard stood in the mouth of the corridor, blocking off their retreat.

-TMNT-

Joe stared at the sight before him in horror. He hadn't expected to find any real trouble here, and certainly not to see Mack walking about loose. He froze, barely registering the other shadowy figures before him. He saw Mack's body flow from upright to four-legged as the creature lunged straight for his throat. He had no time to aim as he pulled out his new gun and squeezed the trigger, praying that he hadn't left the safety catch on.

-TMNT-

The impact of the shot killed the momentum of Mack's leap, stopping him dead in the air when he was just inches away from the guard. The shot had gone wide, but only just. Instead of hitting the shape-shifter in the chest, the bullet had merely torn through the outer muscles of the shoulder. As Mack fell to the ground, he was aware of the turtles rushing past him to overpower the guard and take away his gun. Within seconds, Joe was lying on the ground several feet away and out cold. Raph stood over him, sais at the ready, but didn't deliver the final blow. Mack blinking slowly, unsure of what he was seeing. As Raph and Leo walked away from the fallen guard, the shape-shifter let his eyes close. His shoulder was on fire, and he was in no mood to puzzle out his friend's peculiarities.

Don knelt at Mack's side, turning him over to get a look at his wounded shoulder. He stared in amazement as it began to close up of its own accord. Mack opened his eyes and flinched away from Don's touch with a growl.

"It's OK, it's only me," Don said, quickly lifting his hands from Mack's side. "Can you get up? We need to move before anyone else gets here. That gunshot must have attracted some attention."

Mack raised himself onto three legs, and managed to limp to the box. He shifted to a more upright form, but it was a slow process. A look of panic crossed his face. He knew he'd be OK to run again within half-an-hour, but they didn't have half-an-hour. They barely had half a minute to spare. Raph was at his side in a flash.

"It's OK, Mack. We can still get out – just tell me the code for the lock."

The look of panic didn't fade, if anything it intensified. Mack shook his head, eyes wide.

"No," he rasped. "I can't stay here – can't!"

Donatello shot a puzzled look at his brother, but Raphael only said, "Go wait by the door, Don." As the purple-masked turtle left, Raph stood in front of Mack and looked him straight in the eye.

"You won't stay here, Mack. Go and stand by the door, and be ready to run – but tell me the code, first."

The panic left Mack's face, to be replaced with confusion. He stared in silence, before managing to say, "...why?"

The turtle laid a hand on Mack's good shoulder. "You're a friend. We don't leave people behind."

Mack seemed to wilt under the weight of Raph's touch. Looking at the ground, he said, "4, 7, 3, 9, 2."

Raph nodded, then pushed Mack gently towards the door, where Don and Leo were waiting.

"Everybody ready?" Mack smiled to himself. That was Leo. Even without Raph's stories, Mack could have guessed that Leo was the alpha of this pack. He couldn't seem to stop himself from taking charge of everything.

"Ready!" called Mikey.

"Yeah, go for it," Raph said. There was silence as the two brothers entered the door codes, then the main gates hissed as they moved apart.

"Run!" yelled Leo, as Don helped Mack through the opening. Mikey sprinted forwards and made it through easily, but Raphael, only a few paces behind, almost got the ends of his bandana caught in the closing gates. Leo grabbed his brother' arm and pulled him clear just in time.

As the five prisoners moved away from the underground complex towards their van, they were watched by Bishop on a monitor in his office. The agent's face was unreadable, but he made no move to summon guards. He watched them until they were out of range, then turned his attention from the CCTV to a small computer screen where a tracking light began to move steadily towards New York.

He allowed himself a barely perceptible smile.

-TMNT-

They had emerged from a tunnel mouth, and found themselves in arid surroundings. Donatello glanced at the PDA he'd borrowed, confirmed their direction, then threw the device back down the tunnel.

"They can probably track these things," he explained. "No sense making life too easy for Bishop and his goons."

Mack walked in his resting form, shuffling on two feet and occasionally touching the hand of his uninjured arm to the ground for balance. He and Raph were walking together, a little apart from the others. The pair were silent for a long time, and seemed to be thinking hard. The shape-shifter's shoulder was healing fast, and he was carrying his arm much more naturally when Raph finally spoke.

"Mack," he said, carefully, as if uncertain how to ask the question, "Why did you think we would leave you, back there? I mean, you saw how I got my brothers out, right? You know I wasn't going to leave them behind – why would we leave you?"

Mack blinked, surprised. "They're usefu'," he managed, at last.

Raph frowned. "Useful?" he repeated, disbelief in his voice. "What's that s'posed ta mean?"

Mack sighed. He would've preferred to have this conversation in more human form, but he was exhausted from his rapid healing. He knew that if he tried to change shape now, he wouldn't have the strength to keep walking. So, after some thought, he said, "Usefu'. Don, knows com... com... knows stuff, Mikey's fast, an' Leo knows s'ra'gey. St'a'gy. S'ra... how to no' get caught," Mack puffed out a breath after this list. He hoped Raph got the picture, because he didn't think he was up to any more explaining.

Raphael felt his jaw drop. After everything he'd told Mack about his family, did the creature really think that he'd only saved his brothers because they were useful? He didn't even know how to begin explaining things to someone so, so… he didn't even know how to describe it! Where did you start, against an attitude like that? Fortunately, at that moment, Don wandered over from where he'd been talking to Mikey, and interrupted them.

"Mack, were you ever human?" he asked.

The sudden change of subject caught Mack by surprise. "Wuh?" he said.

Don didn't seem to register Mack's reaction. "Only, I've noticed you have trouble talking when you're in your more animal shapes, right?" he said, the light of scientific investigation in his eyes. "I think it's because you're trying to speak like a human, but your animal forms don't have the right type of face muscles. Did you always know how to talk, or did Agent Bishop teach you?"

Mack growled at the mention of Bishop's name. "I know. He no' teach. Hah!"

Raph opened his mouth to interpret, but Don seemed to have understood.

"I thought so," he said. "It shouldn't be too hard for you to learn how to use your animal muscles to speak. You should ask our father, Master Splinter, for some advice. He's a mutant rat, and he doesn't have any trouble talking – in English or Japanese. He's away visiting right now, but he'll be back in a month or so." Don looked at his brothers. "Mack can stay with us for a bit, right?"

Leo hesitated. He was always cautious about bringing strangers to their home, and would have preferred to know more about this "Mack" before letting him near the Lair. Mikey, however, was delighted at the prospect of a new friend.

"Sure! Our casa is your casa, right, dude?" he said, flinging an arm casually around Mack's shoulders.

The effect was electric. Mack sprang forward as if he'd been stung, spun round and dropped into a defensive crouch, eyes wide and flickering between all four brothers. There was a tense, awkward moment.

It was broken by Raphael slapping his youngest brother upside the head.

"Knock it off, Mikey!" he snapped. "When you gonna learn, not everyone's as into hugs as you are?"

Mack cocked his head, curious, but his hackles settled back down and he straightened up as much as his current form allowed. He seemed embarrassed, but managed to look the question at Leonardo, as leader of this pack: May I?

Leo seemed to consider for a moment, then nodded.

"If you wish to stay with us, you are most welcome," he said. His tone was perhaps a little stiff, but the invitation was genuine. Mack nodded, and followed the turtles away from the only home he'd ever known.

He didn't look back.

Continued in Part Two: Unnatural