The True Names of the Detectives are not revealed, but Mash claims she is able to tell. Sherlock Holmes, said to be history's greatest detective, paved the path for thousands of skilled detectives to follow. These detectives are but Phantoms, but they are able to manifest in Shinjuku through William Shakespeare's First Folio and Hans Christian Andersen's Märchen Meines Lebens creating a "derivative work." Two hundred are summoned in total. Four of the detectives take a ghostly form, while the rest merely drift around as formless spirits.
- Round-Faced Priest (丸顔の神父?)
- String-Fiddling Old Man (紐をいじくる老人?) - Claims he would like to argue in Moriarty's defense if not for the world-ending situation.
- Shaggy-Haired Professor (もじゃ髪の紳士?)
- Straight-Laced Gentleman (生真面目な紳士?)
- Belgian (ベルギー人?) - Claims to surpass Holmes, so he refuses to appear. The Round-Faced Priest claims he will still help them as one of the formless spirits.
They appear in the form of Shadow Servants. They are incapable of directly attacking anyone, but that would be the same as a Phantom or Heroic Spirit due to their innate natures. None of the detectives summoned are said to be worth summoning in a regular Holy Grail War. While they don't compare to the original, they "shine brighter than any Heroic Spirit" when facing James Moriarty after defeating and absorbing Holmes.