This is the 44th of 48 Bowery Boys movies. And, being one of the later ones, Leo Gorcey isn't in the film and was replaced by Stanley Clements as leader of the gang.
When the story begins, Duke (Clements) is convinced that the landlady is being bilked by a local hypnotist. The hypnotist claims to be able to take people back to previous lives through his services and so it's not surprising Duke assumes the man is a crook. Soon, he and the gang arrive at the hypnotist's apartment, as he's having a party for the press...and they pretend to be from a local paper. Duke challenges the man to hypnotize and regress him...and nothing happens. But Sach is hypnotized and he recalls being a 17th century tax collector. This tax collector, according to this regression, bested Blackbeard while gambling and obtained his treasure map. Now, back in 1957, Duke insists that they research more about this tax collector so that they can, perhaps, find the treasure.
This is a most unusual installment because Sach is, uncharacteristically, not all that stupid. In fact, he seems pretty clever at times! As for the regression bit, it's not unusual as Sach had all sorts of strange things happen to him in the later films in the series....and this is no stranger than most! Overall, mildly enjoyable and mindless fun. Better than usual.
By the way, there really are hypnotists who claim they can regress people to previous lives or to in utero recollections. Their claims are unproven and are very dubious to say the least.