Preface:

I wanted to write a scary bamf!Simon and the idea came to me that the things he may have done with the underground may have been on the darker side of things. He's undisputedly a medical and surgical genius, and the damage he could inflict on a person were he so inclined can be frightening to think about. So here we have an AU scenario where Simon Tam was a torturer and interrogator for the Underground before his sister could be rescued, and this shady chapter of his past is brought into the open when the crew of Serenity of encounters a face from Simon's dark past...

CAPTAIN Malcolm Reynolds liked to think that not all of clients turned out to be the scum of the 'verse, but as his luck had been turning out lately, it seemed that scum was the only way to get paying jobs lined up. However there was always a risk when dealing with scum, and that was when the greater percentage would attempt a double cross or try to skimp on pay. These situations, while undesired, and often unpleasant, could usually be dealt with well enough.

It wasn't until the members of his crew became imperiled that Mal would have doubts. And he was having some now.

The cargo had been secured, and payment had changed hands. And then, in the scuffle that had followed - "Why does it never go smooth?" - their adorable mechanic had been taken by the opposing force, and the man they had obtained in retaliation was proving immune to their usual interrogation tactics. Apparently the man backing the operation was scarier than Jayne, Mal, or Zoë either one on one, or in a combination.

And time was running out.

A thought occurred to him - perhaps the ship's resident rich boy doctor had some sort of compound on hand that could loosen their prisoner's tongue. While he would normally be reluctant to put the good doctor into a possibly violent situation, sometimes there were more important things than Core-bred sensibilities. And he was sure that Simon would agree that Kaylee was one of them.

...

It wasn't the first time that Doctor Simon Tam had been asked to perform an interrogation, but it was the first time he had been given such a task since his time with the Underground. It was also the first time he had been asked to do so with medication. Glancing at the captain out of the corner of his eye as he loaded up a tray with various vials and sterile syringes and scalpels - some of which may act as a sort of truth serum in high dosages - Simon asked, "do we at least have this guy's name?"

The captain grunted a reply, arms crossed as he led the way out of the infirmary to the cargo bay, Simon following closely behind. "His name is Dawson Richards. That's all we got a'fore he clammed right up."

Unseen to Malcom Reynolds the surgeon's head snapped up. This would be easier than he thought.

...

Richards was not a brave man. But in the past he had worked alongside the underground movement on Osiris as a cleaner for their interrogator. And these people, while on any other person their threats and posturing would have a grown man spilling his guts in seconds, paled in comparison to the sheer ruthlessness and gore he had cleaned after in the past. And while he normally wouldn't stick his neck out in such a situation, his current employer had a long political arm. With his large funds, and on the event of his survival he did not want this arm reaching after him.

Footsteps sounded above him on the catwalk overlooking the cargo bay. From where he had been chained to some metal supports he could make out the ship's captain bringing down someone else to take a crack at him. He grit his teeth. Even if he had seen far worse, being beat on was never pleasant.

And then the second man stepped out from behind Reynolds and he felt his blood drain from his face.

"Gorram it! It's you!"

His worst nightmare stood before him in white doctor's scrubs a deceptively bland expression settled on his face. He set down a metal tray on a crate just beyond Richards' reach, and the thug felt himself start to hyperventilate as he caught the winking of the overhead lights on a collection of needles and scalpels.

He was vaguely aware of captain Reynolds giving the doctor a puzzled look, and relaxed marginally. The crew didn't bring out Simon Tam to torture him...they didn't know about the shark in their midst.

The doctor stepped forward and crouched down so that they could see eye to eye. "Dawson," he began, and if that voice didn't give him chills, sending back to the bloody past...

"The girl that was taken, I might be a little bit in love with her."

Oh shit. If there was thing he was even more afraid of than the frightening Doctor Tam, it was an angry Doctor Tam.

"Help me out, would you?"

He stayed silent for naught but a moment as the doctor straightened and retrieved a syringe from the tray and a cotton swab. He gripped Richards arm in strong, cool fingers and began swiping over an area in his inner arm. His breathing grew harsh and shallow as the tip of the needle was brought to rest against his skin.

Dawson Richards bit down on his lip hard enough to draw blood in order to keep his mouth shut. However his remaining resolve was destroyed utterly upon the next sentence Simon Tam spoke.

"Brings back old times."

He turned to the captain and opened his bloodied mouth. "I'll talk, I'll talk! Just keep him away from me!"

...

Simon finished looking over Kaylee, turning to the crew with a small smile as he announced her clean bill of health. He watched, content, as she gave him one her brilliant smiles and dashed off to commiserate with Inara. Slowly, the others drained out of the infirmary as he began to tidy up until he heard the door close firmly behind them.

"I suppose now is the time for an explanation."

From behind Malcolm Reynolds replied. "You'd be correct. There are many a thing that can put terror in a man as that piece of go se had in him, but I'd like to know how a soft Core-boy medic like yourself got into that category."

Simon steeled himself. Despite knowing that this was coming he was leery about the aftermath of this revelation.

"When I was putting together the plan to rescue River I ended up doing some things for the Underground in order to build a reputation among them. In order for the rescue to go down I needed their contacts and their respect. Just throwing money at them wouldn't be enough to get myself into the position to organize an operation of the scale I was planning. And, well..."

Here he paused, just letting a little of the fear and hopelessness he had felt in those days wash through him as he gazed somberly at Mal.

"What does a surgeon do to contribute to a shady terrorist organization?"

Comprehension seemed to be dawning upon Captain Reynolds, who seemed to look a little green.

"Yes...well suffice to say that Dawson Richards worked with us back then, and was mainly responsible for cleaning up after my..." Simon grimaced, "work."

He couldn't look at Mal, afraid of the disgust and recrimination he was sure he would find there.

He heard footsteps as Mal turned to leave. "It's been said before Doc. You ain't weak."

This wasn't the end of it, but for the first time in a long while Simon felt something like closure.

Afterward

So it's official. My headcanon now has Simon as being a former torturer for the Underground. Why, brain, why?