Lieutenant Patrick Porter had been sitting in the interrogation room for hours, waiting for the agents to question him. He knew they were making him wait, hoping to break him down. Trouble was, it was working.

Finally the door opened and Tony and McGee walked in. Tony sat in the chair across from the lieutenant while McGee leaned against the wall next to the two-way mirror.

"So, Lieutenant Porter," Tony said, "do you want to tell me the real story?"

"What do you mean?" Porter replied nervously. "I told you the truth."

Shaking his head the agent chuckled. "No, I'm afraid you didn't. You see, Lieutenant Walker ordered pizza that night and the delivery guy said he saw someone watching tv while Walker paid him. He said that someone was you."

"Identified you from a picture," added McGee.

"And that's not all, Lieutenant," continued Tony. "We found the weapon, one of Lieutenant Walker's Eiffel Tower statues."

Porter's already pale face turned whiter. "I didn't stab him with anything," he said shakily. "We fought, yeah, but I didn't kill him."

"What did you fight about?"

"It was stupid, okay?"

Tony nodded. "Okay, it was stupid. Just tell us what you fought about."

"Stevie had a chip on his shoulder," Porter said, "a real big one. He thought he was better than everyone because he came from money and his father is a Rear Admiral. We got into an argument over money."

"What happened?" Tony urged the man to continue.

"Stevie was talking about how much his car cost and what he was going to do when he got married and left the Navy," Porter said. "I come from a middle-class family. My folks both work in a factory. I was arguing with him about how hard it was out there for the poorer folks, how the middle class was disappearing. It got kinda heated, and I punched him. We started fighting, he fell and I stormed out of there. I didn't even look back. I didn't stab him, I swear."

There was a knock on the door. McGee went to answer, spoke quietly to the person outside, then turned to Tony.

"Boss, could you come out here please?" he asked.

"Excuse me," Tony said to Porter.

Abby was waiting for them outside. "I've got bad news, Tony," she said.

"What?"

"The only prints on the statue belonged to Walker, and Porter's DNA didn't match the DNA of the blood on the floor."

"What does that mean?" asked McGee.

Tony stood thinking for a moment. "McGee, have someone take Porter home. Abby, let's go."

"Wait a minute," McGee protested. "You mean we're going to let Porter go?"

"He didn't kill Walker, McGee," replied Tony. "Apologize to him for me, okay?"

"If he didn't kill him, who did?"

"Get someone to take him home and meet us in the lab."

The whole team, minus Ducky, was down in the lab. Abby had been working on a simulation program with Tony, programming in what he thought had happened.

"Who do you think killed Walker, Tony?" asked Ziva, curiously.

"Here's what I think," replied Tony, motioning for Abby to start the simulation while he explained what happened. "Walker and Porter were sitting around, eating pizza, watching the game on tv. The game is over, or something, and they start talking about future plans. Walker starts bragging about how easy he's going to have it and Porter gets upset. Never talk politics, by the way, leads to nothing but trouble."

Abby and McGee snickered, while Jimmy nodded his head in agreement.

"So, they fight, right?" The computer simulated people grapple onscreen. "Walker falls and lands on one of his statues, but Porter is already on his way out the door and he doesn't bother to turn around and see if the guy's okay. Walker gets up and stumbles around, goes out onto the balcony for some reason, maybe he needs some air. He pulls the statue out and drops it, it falls off the balcony. Then Walker stumbles back into his apartment, falls down and dies."

"That's why the only prints on the statue are Walker's," Ziva said.

Tony nodded. "Yes. This was an accident."

"What about the DNA?" asked McGee.

"Now that," said Tony, "is a mystery."

"Maybe not," said Jimmy, thoughtfully. "Lieutenant Walker could be a blood chimera."

Tony turned to Jimmy. "Blood chimera?" he asked.

Abby's eyes grew big with excitement. "Yes, a blood chimera!" she said excitedly. "Jimmy, that's brilliant! That's inspired! We have to do the tests."

"Maybe he's a tetragametic chimera." Jimmy was getting excited too. Tony, McGee and Ziva stared at them, confused.

"What are you two talking about?" asked Ziva.

"You know what a mythical chimera is, right?" Abby asked. "It's a creature that's part goat and part lion, with a serpent tail. Anyway, the most common form of a human chimera is a blood chimera. That's when fraternal twins share part of the same placenta, they exchange blood stem cells. So a person can have AB blood, but be either A or B genetically "

"When two embryos fuse to form one embryo, the result is a tetragemetic chimera," continued Jimmy. " Their body is made up from two genetically distinct lines of cells derived from a total of four gametes – eggs and sperm. A person can show no signs, or they can have different color eyes, one blue, one brown. There have been cases where they found structures of both the female and male reproductive systems and as a result the person had cells of both sexes in their bodies."

"This is so cool," raved Abby. "We can write a paper together, Jimmy. We can be published." She jumped up and down excitedly.

The three agents left Abby and Jimmy jumping around in the lab and headed back to the squad room.

"Well," said Ziva, once they were on the elevator. "That was interesting."

"Weird case," agreed McGee. "At least Lieutenant Walker wasn't murdered."

"No," agreed Tony, "it was a stupid accident. That's not much of a comfort to his family, but at least they have closure."

Epilogue:

Two days later the Director called Tony and his team to her office for a briefing. The agency had received some intelligence about a possible terrorist plot against an unknown target on the west coast. Information was sketchy, but they were able to determine that the plot involved a Navy battle cruiser and a western port.

The team was seated around the conference table in the Director's office, getting briefed.

"We're bringing in an expert in military operations and terrorism," said the Director, "he'll be working with you, reporting directly to me."

Ziva started to protest, "We don't need an expert in terrorism; I have a great deal of expertise in that area, you know that."

"Ziva's right," agreed Tony. "We don't need someone looking over our shoulders and telling us what to do."

"This person won't be there to keep an eye on you or to do your job," explained Sheppard, "he'll be there to offer his expertise and assist you in any way you see fit." She pressed a button on her intercom. "Cynthia, send him in."

The door opened and Gibbs walked in.

"Gibbs!" exclaimed Ziva. Tony and McGee grinned at their former boss.

Gibbs grinned at the delighted expressions on their faces. He would never admit it out loud, but he missed his old team. He not only enjoyed working with them, watching their growth proudly, but he enjoyed their company.

"Are you coming back to NCIS?" asked McGee.

"No," replied Gibbs, "I'm working strictly as a civilian consultant."

Tony turned to McGee and said, "They call him Mr. Gibbs. Ow! Hey, assaulting a Federal Agent, Boss, that's a felony."

"Don't call me Boss."

FIN

A/N: Tony has come through this totally unscathed. Yay me! Thanks again to my wonderful beta Rinne, she rocks(mwah)and my sounding board andmuse, Research Geek.