Star Trek: The Next Generation/Recap/S3/E07 The Enemy

Those sneaky-ass Romulans are up to no good again, and this time they're hanging about a hellhole of a planet called Galorndon Core.

The A plot is that Geordi is stuck down on the planet with a Romulan crash survivor, and the two of them will have to work together if they want to survive. Since transporters and scanners don't work on the planet (like every third planet they come across), Wesley manages to come up with a beacon they can send down that Geordi will be able to see with his VISOR, and configure the beacon into a transporter signal enhancer (with much of the audience no doubt wishing Geordi had died rather than giving Wesley another win). Unfortunately, the planet's magnetic interference has rendered Geordi truly blind, so he will have to completely rely on his tenuous partnership with the Romulan.

The B plot is that the Enterprise is host to another Romulan crash survivor, and he needs a blood donor to live. In a shocking twist designed to create drama, out of the 1,000+ people on the ship, only Worf is a compatible donor. (This is often mis-cited as an actual blood transfusion, causing people to harp on Star Trek's No Biochemical Barriers thing. Crusher actually says she only needs a part of Worf's blood to synthesize a replacement for the Romulan's, so it's not quite as bad as all that.) Considering that his entire family was slaughtered by Romulans (which the Romulan himself seems quite proud of when Worf talks to him), Worf isn't exactly in a generous mood with his bodily fluids (as in he likely wouldn't even use certain of them to douse the Romulan if he was on fire).


 * Depending on the Writer: Starfleet's notorious yo-yo medical science strikes again. Crusher apparently can't just clone more Romulan blood, or culture the part of it she needs, or use a synthetic substitute, she has to have actual blood from Worf to create the infusion the Romulan needs (or else the forced drama of the B plot wouldn't work).
 * Enemy Mine: The entire A plot. In fact you can tell they had to resist the urge to just use this as the episode title.
 * Informed Wrongness: It's not necessarily Worf's refusal to help that falls under this trope, but rather the fact that everyone acts like it's completely on Worf. All other involved parties, especially Dr. Crusher, conveniently ignore the fact that the injured Romulan specifically said he would refuse any transfusion or treatment if Worf were involved. (But then, Dr. Crusher isn't particularly known for respecting the wishes of others, including her patients.)
 * No Biochemical Barriers: Not as big an example as many discussions of the episode claim. Worf actually protests the unlikelihood of a Romulan needing a blood transfusion from a Klingon as opposed to any of the Enterprise's Vulcan crewmembers. Crusher explains that it's actually only part of the blood she needs, and that the two only have several (apparently rare) genetic markers in common.