Susan Ivanova discovers a derelict spaceship in hyperspace. They tow it back to Babylon 5, then strange things start happening. People are being telepathically taken over by aliens from another (third)space.
Acting
Claudia Christian carries this entire thing on her back.
Practical Effects
The Thirdspace creature design is gloriously gross practical effects.
Production
Budget constraints visible, ambition undeniable.

Director
Jesús Salvador Treviño
Trivia, insights & behind the scenes
This was the first Babylon 5 TV movie produced after the main series ended, filling the gap before Crusade. They had to rebuild sets from storage.
The Thirdspace entities are essentially Babylon 5's take on Lovecraft's cosmic horror—ancient, incomprehensible, and the Vorlons were scared of them. That's the real flex.