Just the Facts, Ma'am: Horrible Harry at Halloween by Suzy Kline.
It's Halloween, and Ms. Mackle and her third grade class are in costume for the holiday. Ms. Mackle is a full-dress witch, with raisins for warts and a tall black hat. The kids' costumes range from a fairy with a wand and pixie dust, to a bear with thick (and hot) fur, a doctor in scrubs, and even a centaur with its hind hooves on roller skates. Despite the variety, however, the question of the day is--"What's Harry going to be?"
As the kids watch the clock, they reminisce about Harry's earlier costumes: in Kindergarten he was a spooky Count Dracula; in first grade he was a slimy Loch Ness Monster; and in second grade he was a snake who was late for school because he had to squirm all the way across the playground to get to the door.
Just as the late bell is about to ring, Harry Spogger, "Horrible Harry," steps into the classroom. The class is totally boggled. There stands Harry, wearing a suit and tie and sporting polished black shoes. Where's the long-awaited costume?
Harry pulls out a shiny badge with the number 714 and pins it to his lapel with a flourish. "I'm Sgt. Joe Friday of the L. A. Police Department," he announces. As the confused class looks blank, Ms. Markle laughs and tells the class all about Joe Friday, the famous detective in the old television police show Dragnet.
The disappointed class gets to see Joe Friday in action after lunch, however, when fairy Mary discovers that her magic pixie dust (a.k.a. baby powder) is missing from its shiny box. Harry, alias Joe Friday, whips out his notebook and begins to interrogate the robbery victim. Harry, who "has a nose for the clues," quickly sniffs out the smell of talcum on Sidney and deduces that he's the perpetrator, having sneaked a bit of "pixie dust" to soak up the sweat under his fuzzy bear mask.
As the grand finale for Halloween Day, Ms. Mackle reads "The Headless Horseman" to the class, and everyone follows Harry's lead in pulling their costumes up over their heads to greet their music teacher with a headless class (and teacher) when he opens the door!
At Accelerated Reader level 3.2, Suzy Kline's Horrible Harry at Halloween provides "just the fun, Ma'am" for the beginning chapter reader at Halloween.