Milky Holmes is the fictional heroine quartet of girl detectives of the series franchise. They serve the Holmes Detective Academy long enough to be well-known and respected. All of their achievements proved that they can win to any obstacle standing on their way — friendship-wise and when it concerned their intelligence.
But when one day, all of them lose their precious Toys, they become the school's laughing stock; losing all their VIP privileges and even their beautiful suite, Milky Holmes has to face a huge challenge. Losing Toys might be easy, but how about re-gaining them?
Worth noting is that in the anime, Opera Kobayashi does not appear. In the Visual Novels, Opera is the main protagonist who runs the Milky Holmes Detective Agency and guides the four girls.
In Tantei Opera Milky Holmes 2 Visual Novel, a new female protagonist named Ellery Himeyuri is introduced. She is put in charge of the detective agency after suddenly gaining her own Toy.