Lieutenant Worf stood in Holodeck 4, watching LaForge and Data as they wandered through the three-dimensional holographic recreation of the interior of the Mok’tagh. The isolinear rod had provided enough data to make this simulation possible, and LaForge thought it was the best way to determine what had happened and why. Worf looked around, noting how different the interior of the Mok’tagh was compared to the Enterprise; spartan and cold, with no thought given to aesthetics. He felt his Klingon blood stir. What would it be like to serve aboard a ship such as this–a warrior’s ship–rather than a ship of exploration like Enterprise? He glanced at the PADD in his hand and growled in exasperation.

Data looked up from the holographic EPS conduit he was examining. “Is there a problem, Lieutenant?”

Worf’s eyes narrowed. “Commander, we are wasting time. The Klingons will have little regard for–” he gestured at the simulation, “this. “

“We are using our most effective method of determining the cause of the accident aboard the Mok’tagh given the data we have at our disposal. I fail to see how that is an inefficient use of time.”

“The Klingons have already decided Lieutenant Barclay’s guilt. They will not be swayed by holograms.”

“Maybe they won’t have to be.” LaForge sounded puzzled. “Worf, besides Barclay, who else was on the engineering detail?”

Worf regarded the PADD. ” Enisgns Mokta and Ramirez, Crewmen Steinway and Cortland, Specialist J’zhara.”

“That’s six,” LaForge said, “and they’re all here. But that makes no sense. The conduit that exploded was one level down. None of our crew were anywhere near there.” Geordi regarded his tricorder. “Wait a minute. This shows some modifications were done from the engineering deck.”

Data spoke. “Computer: please display the engineering deck of the Mok’tagh, same time stamp.” The room shimmered and the EPS conduit tubes were replaced with the environment of the Klingon engineering deck. Several Klingons were manning their positions. All seemed calm and in order, except for one thing.

“Guys,” said LaForge, “who the hell is that?”

“A Vulcan?” Picard asked. “Explain.”

“We don’t know, sir,” answered LaForge. He regarded the display screen in the observation lounge, where the image of a tall, middle-aged Vulcan man in a Starfleet engineering uniform was pictured. He looked around the room at the senior staff, seated once again at the conference table. “One thing’s for sure, he’s not an engineer on this ship. I’ve never seen him before.”

“Someone not in Starfleet, then?” asked Troi. “There are plenty of civilians aboard.”

“Computer,” Picard said, “How many Vulcans are presently aboard the Enterprise?”

“There is a total of 84 Vulcans aboard,” the ship’s computer answered.

“Are all accounted for?”

“Affirmative.”

“Identify this person.” Picard commanded.

“Identity unknown.”

“We inquired already, sir,” Data said. “There is no record of this individual ever setting foot on the Enterprise.”

“Near as we can tell, he must have split off from Barclay’s team and went to the engineering deck on his own,” said LaForge. “That’s probably where the sabotage occurred.”

Barclay protested. “But he didn’t split off! He was never with us, Commander! I’m sure of it!” He seemed to realize he was shouting, and lowered his voice. “I think I would have noticed someone I don’t know on my team…”

“As you were, Lieutenant,” Riker said. “No one in this room doubts your word.”

“That is about to change,” said Worf, as the doors to the observation lounge opened, signaling the return of the three Klingons.

“Well, Picard?” asked B’rul. “Are you ready to hand your officer over for interrogation?” Picard gestured to the empty chairs again. After a moment, B’rul sat, the others following suit.

“It seems, Captain,” Picard began, “that we have something of a mystery on our hands.” He briefly explained the situation to the Klingons. “We strongly suspect this man,” Picard indicated the image of the Vulcan on the screen, “is our saboteur, but we have been unable to identify him.”

“Not surprising,” laughed Gr’val. “One Vulcan looks much like another.” His remark was met with stony silence. Even B’rul looked disgusted. “Shut your mouth, you ignorant fool,” he said in Klingon. Gr’val flushed and stared at the table.

“What are you playing at, Picard?” demanded B’rul. “This Vulcan transported to the Mok’tagh from the Enterprise. He’s one of your engineers!”

“I assure you, he is not,” Picard said. “We have no record of this individual ever being aboard this ship.”

“Lies!” shouted Gr’val, pointing at Picard.

B’rul turned to him slowly, his eyes flashing. He did not bother to address his adjutant in the Klingon language this time. “If you dare to speak without my leave again, you will not leave this room.” Gr’val clamped his mouth shut. Dresa smirked.

B’rul stood up and approached the viewscreen console. He stared at the unfamiliar interface for a moment, then began to access the data from the isolinear rod. “These are the transportation communications between the Mok’tagh and your ship,” he said.

Everyone listened as the logs began to play. “Enterprise to Mok’tagh,” came the voice of Transporter Chief O’Brien. “Six to beam aboard.”

“Acknowledged,” came a gruff Klingon voice. A moment later, the whine of the transporter could be heard.

“Transport complete,” came the Klingon voice again.

Barclay began to speak. “Yes, that was when we beamed over. But there was no Vulcan with us. Specialist J’zhara is Andorian and Ensign Mokta is Tellarite, the rest of us are human–“

“Silence!” B’rul said, holding up his hand, as O’Brien’s voice began again.

“Enterprise to Mok’tagh: looks like we forgot one. He’s on his way over now.”