A call on the hotline takes the Mystery Math Squad to a construction site. According to Paul Parker, their project is at a standstill because the area is haunted. Addie, Linus, Trixie and Devon have their hands full multiplying and dividing steps, window panes and wall carvings to solve riddles. The gang gets a real adventure for their history project; complete with an old structure, a ghost and a disappearing Trixie! Will the mystery math Squad's math skills help figure out what's going on in the middle of the woods?