Many of the other reviewers here seem pretty well versed on the star and these kind of films, but I'm approaching both Hay and British comedies from this era in general as a newbie. Judging from the plot synopsis written here, I was expecting a merging of comedy with old dark house horror along the lines of HOLD THAT GHOST (made the same year in the States), but this is pretty much just a straight comedy that happens to take place in a spooky setting. During WWII, St. Michael's school for boys has to move to a more secure location - a large, gloomy, remote, rat-infested castle located in Isle of Skye in Scotland. Staff and students show up and get settled in, and uppity, bumbling, fast-talking teacher Will Lamb (Will Hay) is immediately assigned the position of science teacher despite being grossly incompetent to handle the position. Lamb is quickly befriended by a goofy colleague (Claude Hulbert) and, because of his unconventional approach and manner, manages to win over the boys in his class. But soon enough, multiple problems arise for our hapless hero. For starters, nasty teacher Mr. Humphries (Raymond Huntley), who seems a little overly eager to climb the professional ladder, tries to convince the school headmaster (Felix Aylmer) to fire him. Secondly, because of its sordid history, the creepy castle caretaker (John Laurie) seems dead certain that the castle is haunted by a malignant spirit. Third, several people end up getting killed, with the ominous "phantom pipes" (bagpipes) signaling each death. Who's responsible; a vengeful human or a centuries-old ghost?
One noticeable difference between this and concurrent comedies from the States is the presentation of Hay's character. You didn't too often see (in American movies from this period) an authority figure/bumbling hero who flagrantly lies, is incompetent in his line of work, drinks whiskey with a bunch of underage students and acts like he's going to haul off and slap or kick his pupils when they say something he doesn't like. Yet somehow, Hay manages to come off as utterly charming and likable. You can see why the pupils take a liking to him. The entire supporting cast; particularly Aylmer and Charles Hawtrey, as the brainy and outspoken student Percy, was excellent. As far as this functioning as a murder-mystery, it does a fairly good job of that as well. There's a lively finale making good use of trap doors and secret passageways. When the killer's identity is revealed it's also a genuine surprise. Though obviously a low-budget and set-bound production, it's fairly well staged and has a decent screenplay with plenty of amusing dialogue and good comic situations to put our heroes in. All in all, it's a pleasant and entertaining way to spend 78 minutes of your time.