Investigative ointment

Investigative ointment is a homemade chemical tracing mixture devised by Jupiter Jones to turn an unseen person’s contact into visible evidence. Its white coating appears harmless, but contact with it produces indelible black spots on the hands within half an hour. Used first to test Fenton Prentice’s account of a mysterious intruder and later to mark a ransom parcel, it helps replace apparently supernatural uncertainty with a physical trail.

Preparation and Properties

Jupiter prepares the mixture in the tiny laboratory the boys fitted out. He displays fine white crystals in a ceramic jar, adds a few drops of water from a flask, and stirs the crystals with a small plastic spoon. He identifies them as a metallic compound he had read about in an old criminology book and explains that they dissolve in water. He then takes a tube of thick white ointment from a drawer and mixes a generous amount into the solution, slowly and thoroughly. He says he has kept the ointment for emergencies and that it absorbs water.

The resulting paste is creamy and white. Jupiter calls it magic ointment, but its operation is chemical rather than supernatural: it can be spread on an object, remain clean-looking there, and transfer a trace when someone touches it. The treated person’s fingers develop black spots that cannot be washed away. Jupiter’s stated time window—within half an hour—makes the mixture useful not only as a marker but as a way to connect recent contact with a particular object.

The surface being treated matters. Jupiter warns that the chemical reacts with metal and might damage copper or brass, while ceramic is safe. That constraint shapes his first test: the knobs on Fenton Prentice’s desk drawers are ceramic, making them suitable both for the chemical and for catching the suspected intruder’s touch. The ointment is therefore not a universal coating; its practical use depends on choosing an object that can bear it without damage.

The Test in Prentice’s Apartment

Fenton Prentice had told Jupiter that he sometimes sensed a shadowy presence in his apartment and had once returned to find his desk gone through. The apparent intruder seemed able to come and go even when Prentice was present, and Prentice doubted that a physical person could be responsible. Jupiter proposes a test instead of accepting the ghostly explanation: with the apartment door locked, he coats the ceramic drawer knobs and leaves. If someone opens a drawer while they are away, the ointment should mark that person’s hands.

When the boys return, Jupiter finds the ointment smeared and concludes that someone has opened the desk. The trace changes the nature of the question. It indicates contact by ordinary, solid human hands, rather than proving the presence Prentice had feared. Bob Andrews fetches a paper towel, and Jupiter wipes the knobs clean before asking permission to inspect the desk.

A second trace extends the test from the desk to the exit. Jupiter had not treated the apartment’s door knob, but notices smudges on it. He infers that the intruder opened the door to leave. The deadbolt bears ointment on its outside, showing that the door was locked behind the departing person. From that sequence, Jupiter concludes that the intruder had a key. Prentice objects that the lock was special and that no one should have a key, but the marked bolt makes the supposedly impossible access a practical security problem.

The Ransom Parcel

Jupiter later adapts the same method to the theft of the Carpathian Hound. He reasons that Fenton Prentice knows where the stolen object is, so there is no reason to deliver real money when a ransom is demanded. Instead, the investigators can prepare a parcel treated with the ointment. Even if they do not see the person collect it, the black spots should identify whoever handles it. Jupiter also believes the burglar must be a tenant in the building, since the culprit knows details such as Gwen Chalmers’s fondness for chocolates and Mrs Bortz’s early-morning shopping routine. Those details narrow his suspicion, while the treated parcel is intended to provide a physical test.

The package is ultimately found still sealed in a closet, and Jupiter tells Murphy that the ointment will mark his hands even if he has disposed of the parcel. Murphy looks down at his hands as Sergeant Henderson steps forward to arrest him. The evidence presented here does not describe the spots actually appearing; the ointment’s predicted effect, the parcel’s recovery, and the surrounding deductions bring the trap to its conclusion.

What the Trace Establishes

The ointment’s value lies in the difference between an invisible act and its material remainder. A person can leave a room without being seen, and a parcel can be handled outside the investigators’ sight, but the coating turns contact into a trace that persists after the moment has passed. At Prentice’s apartment, its smears help reconstruct an entry and exit: the desk was opened, the door was used, and the deadbolt was secured from outside. At the ransom stage, the same principle is aimed at the person who takes the parcel rather than at the route through the apartment.

The mixture does not, by itself, explain every part of the case. Its marks are evidence of contact, while Jupiter’s conclusions about keys, access, and identity depend on reading those marks alongside other facts. Murphy’s hospital presence, for example, had seemed to offer a private alibi; Jupiter later explains that Murphy staged the fire in his apartment to get into hospital and took advantage of the nurses’ routines to slip out. Murphy had borrowed money from Harley Johnson’s account for stock-market speculation, lost it, and needed ten thousand dollars to replace it before Harley came of age the following month. Those circumstances explain the ransom motive; they are not chemical properties of the ointment.

The object’s narrative role is to make a clue legible without making it magical. Its nickname briefly suits Jupiter’s theatrical presentation, but the recipe, material limits, and delayed stains give the device a concrete logic. A clean white coating becomes conspicuous only after someone touches it. In both deployments, the ointment shifts attention from what an unseen culprit claims or appears to be toward what a hand has physically done.