Space Quest IV.5 is a freeware adventure game set in the familiar Space Quest universe, first conceived by Mark Crowe and Scott Murphy a.k.a. the "Two Guys from Andromeda". The game was made using the freeware Adventure Game Studio (AGS) engine and borrows most of its artwork from other Sierra On-Line and some Tsunami Media games.
Its aim is to tie up the loose ends between the end of Space Quest IV and the start of Space Quest V. What sets it apart is its unusual use of an over-the-shoulder commentator that shows up from time to time to warn intrepid space janitor and unlikely hero, Roger Wilco, when his actions threaten to disrupt the game's storyline continuum.
As alluded to in the title, Roger is sent back through time after beating his nemesis, Sludge Vohaul, in Space Quest XII and is now trying to return to his home planet, Xenon. He finds his trusty Aluminium Mallard parked in front of the "Bar" on Magmetheus where he left it and sets off on his quest.
So, how did he end up as a Starcon cadet in the next installment in the series... You'll just have to find out for yourself.