My group last night were at the second group of transmitters and had just killed off the trash in the middle. I had just placed turrents near the first transmitter when a TOS dressed science officer and a TOS klingon beamed in and started battling eachother. The Fed officer was allied while the Klingon was an enemy. It was sometime between 10 and 11 pm Central Time. I'm sorry I can't provide more info as this took place almost 24 hours ago now. However, please respond if something like this has happened to you (with, hopefully, more detailed information).
That would be what happened, then... The Triolic Pattern Enhancer has a random % chance of summoning one of several different critters, including, but not limited to, TOS characters (Fed or Klingon), Devidians (the Phantasms are the WORST), a pile of Tribbles, etc.
One Infected run that my fleet completed, we had a TOS Science officer get summoned in, at the very first battle after beaming down (lots of Tac guys with Tac Initiative + Triolic Pattern Enhancers = Lots of use out of them), he followed our group and stayed alive, healing our team, all the way through the mission, until we fought Captain Ogen, where he finally (and bravely) met his end.
The odds of you actually getting a TOS Fed and a TOS Klingon at the same time are pretty low, but that's really cool!