Harry and his detective classmates try to find clues relating to a mysterious locked closet in Room 3B.

The Locked Closet --1 -- The Things under the Door -- 7 -- Volcanoes in Room 3B! -- 13 -- Harry's Discovery -- 22 -- The Hole in the Closet -- 32 -- The Search Party in the Attic -- 40 -- The Mystery Is Solved! -- 49.