Author's introduction and disclaimer. The characters in this story are either the creations of those involved in the production of Star Trek over the past 40 years or are interpretations of what such individuals would be like in the Mirror Universe. I've used some novels as a guide in determining this, but they are not the same people, as it's not quite the same universe. No copyright infringement is intended.
"Captain's log, stardate 58511.2. We've successfully concluded another round of negotiations with the Romulan Empire and are looking forward to a period of R & R at DS9. A very important passenger is accompanying us back."
The Rikers had booked a holosuite reservation with Vic Fontaine from Quark's. Deanna was smiling as she watched her husband playing in Vic's band. Another of the Titan's crew, Wesley Crusher, was having dinner with his mother who was on leave from the Enterprise.
"So, how have things been?" Beverly asked.
"Okay," Wesley answered. "I'll be meeting with Robin from the Excalibur later on. I thought we could catch up on things."
"That's nice," Beverly said. They both noticed the Excalibur's Chief Medical Officer coming toward them. Dr. Selar seemed casually dressed, almost rag-tag, which Beverly knew wasn't like her at all.
"Wesley Crusher?" Selar asked.
"Yes?" Wesley got up, but the Vulcan pressed her hand against his temple and locked him in a mind-meld. "Remember," she told him. She then backed away quickly and pulled out a small, cylindrical device before disappearing in a transporter beam. Dr. Crusher recognized the device from its description in Starfleet reports as the alternate universe's multi-dimensional transporter. So that's who that Selar was.
Wesley seemed in a state of shell-shock. Dr. Crusher was beside herself. She contacted Dr. Bashir about it, and since the Excalibur was also docked, she paged Dr. Selar--the real Dr. Selar.
The Excalibur's CMO showed up and requested permission to mind-meld with Wesley in order to obtain more information. Dr. Crusher said yes, and the Vulcan pressed her hand to his temple just as her counterpart had done. Moments later the Vulcan spoke.
"We need to find my counterpart in the alternate universe immediately," she said.
"Why?" Dr. Crusher asked her Vulcan colleague.
"Because the katra she placed into Mr. Crusher is that of his counterpart in her universe."
"Can't you do anything about it?!?"
"We need my counterpart to reclaim the katra from your son," the Excalibur's CMO answered. "She needs to do it because only she is able to properly sort out the memories of each individual. Because their minds are so similar, this needs to be done within 24 hours or there could be a complete fusion of identities."
Beverly Crusher was ashen.