In January of 2152, Rostov was linked to Captain Jonathan Archer, Commander Tucker, Crewman J. Kelly, and security officer Zabel when they were caught up in a strange, fibrous alien creature's tentacles. (ENT: "Vox Sola")
Later that year, Rostov attempted to reinitialize the plasma flow, after the Enterprise had been taken hostage by the Wisps' ship, but was unable to because the power grid was not charging. When he reported this to Tucker, he noticed that Tucker was acting "wrong", and reported to Captain Archer that Tucker seemed confused, and, in addition, seemed to think Rostov was his superior officer. Later, when Rostov was ordered to prime the deuterium pumps and fire up the warp injectors, his body was taken over by a "Wisp". When Tucker confronted him and asked him if he had any luck priming the pumps, the Wisp/Rostov stated, "I have no idea how to do that. This engine is very complex." He was later escorted to his quarters, where he remained locked until he was freed of the wisp. (ENT: "The Crossing")
Background information Edit
It is likely Rostov originally had the surname "White". He was still referred to as that in a page of the final draft script of "Vox Sola", when that script was first issued. In the same script, Rostov was described as "A male crewman in his early thirties [....] He's an engineer with a mischievous streak and a dark sense of humor."
Rostov was played by actor Joseph Will. Due to the gooey alien which Rostov becomes caught up in during the episode "Vox Sola", Archer actor Scott Bakula coined and used the nickname "Goo Boy" for Will. After the character was introduced in "Vox Sola", plans were made for Rostov to reappear. Will said, "I remember bumping into Brannon Braga on set and him whispering to me that he couldn’t promise anything but they might bring Rostov back a few times if things worked out." (BLANKMANinc.com: The Star Trek Interviews)
In the final draft script of "Two Days and Two Nights", Rostov was given a couple of lines of dialogue in the episode's penultimate scene, though he doesn't speak at all in the final version of that scene. He was scripted to relay news to Captain Archer that, following a rock climbing accident, Ensign Mayweather was going to be fine, with "just a broken leg," and later apologize for missing the shore leave on Risa.
Contemplating why Rostov didn't appear after the second season of Star Trek: Enterprise, Will stated, "Unfortunately for me, they had so many series regulars on Enterprise that the producers couldn’t justify involving peripheral story lines about Rostov the engineer or they didn’t particularly like him." (BLANKMANinc.com: The Star Trek Interviews)