It is the proudest day of Bud Alexander (Bud Abbott) and Lou Francis's (Lou Costello) lives, well, it's the proudest day in Lou's life at any rate as they finally graduate from detective academy. Lou doesn't know how he managed it until Bud mutters an aside to the effect that he slipped the Head twenty dollars, but no matter, they are now able to call themselves fully-fledged private eyes. They move into their office and are tremendously excited about the prospect of solving crimes, and soon enough boxer Tommy Nelson (Arthur Franz) has barged in looking for help - but he's the one on the run...
The huge success of Abbott and Costello Meet Frankenstein was still keeping the box office tills ringing for Universal studios, so what better idea than to pair them with another of their galaxy of chiller stars. After a brush with Boris Karloff, it was decided to tailor a sequel to The Invisible Man to their talents and this self-explanatory film was ther result. Of course, they had already met The Invisible Man at the end of ...Meet Frankenstein, there a cameo by Vincent Price, but this was ostensibly a different character.
As Tommy, Franz didn't get much to do except lend his voice to the special effects, but here those effects really looked as if they were being perfected. Admittedly they still used the old trick of getting the actor to wear a head covering while still in their smoking jacket or whatever, to make it look to the unwary that he had no noggin, but there were innovations here as well. Tommy ends up vanishing after his girlfriend Helen (Nancy Guild) advises him to see her scientist uncle, Dr Gray (Gavin Muir) who so happens to have been left the secret to the special serum by the late Dr Griffin.
Gray is reluctant to allow Tommy to try the serum, but when he and Helen are distracted Tommy injects himself to avoid the police who have turned up at the door thanks to a tip off from Bud. Naturally, Lou is left alone in the drawing room while the boxer undergoes his transformation for some panicky behaviour that had gone down so well before, and because nobody can see Tommy, Lou is packed off to the psychiatrist. There aren't that many of the comedy duo's routines in this one, as most of the humour is in the service of the plot, but they were by this time old hands at this kind of thing.
And look at those tricks: we follow the Invisible Man's cigarette, for example, as he smokes it while walking down a hall, including a puff of smoke when he exhales. And when Tommy, who has persuaded Bud and Lou to help him out, plays a game of cards with them (gambling addicts Abbott and Costello must have appreciated this scene) marvel at him dealing the deck. The setpiece involves a boxing match - naturally - that has the bumbling Lou pretending to be a new prizefighter, except his knockout punches are actually Tommy's, administering the beating but unseen by all. This bit features more mime than anything else, but it's nicely done and is an energetic finale to a film that might not bring the house down these days, but was professional and entertaining. Although the last couple of minutes are among the most bizarre in comedy history, no matter what the era.