Originally published Weird Tales May 1942
Our Narrator works at a drug store as a pharmacist and soda jerk. Mostly the latter. And he hates his job. One evening a sinister-looking dude shows up and has him put together some very suspicious stuff - aconite, belladonna, etc. And asks his to to put it on his account. Being in a sever state of not-giving-a-shit, o.n. complies.
Three days later Mr. Sinister, who's real name is Fritz Gulther, shows up dressed to the nines and pays his bill. And invites o.n. for a drink. There, o.n. tells him he knows what he's up to - black magic!! No no no no no sez Fritz - its just medieval-type chemical recipes. And he's used them to create a brilliant formula that netted him a great job at Newsohm, a chemical corp, and would o.n. like a gig as his secretary? All of this is going promisingly till o.n. notices something odd - Fritz's shadow on the wall seems to be independent of him - it doesn't move with or quite match its originator. When o.n. mentions this, Frtz threatens to bash his skull in.
But, Fritz is back the next day, apologizing and offering the job again. He insists, insists he's not practicing black magic. O.n. agrees to the job offer. But again he notices Fritz's shadow ain't right.
Next day, o.n. goes to Gulther's office and finds a copy of De Vermis Mysteriis. Gulther fesses up: yes he used black magic to get ahead, and yes he knows about the independent shadow. And its growing more powerful.
As they talk, the shadow takes the place of Gulther. O.n. shoots Gulther, but all that is left is an empty suit of clothes.
This little Bloch tale is more characteristic of Unknown, or for that matter, The Twilight Zone, then WT. But nevertheless Bloch was a name by 1942, so his byline was good for sales. This is Bloch in his mature mode; a lot of humor, a lot of misanthropy (I'm not sure Bloch wrote much after 1940 that didn't disparage current trends in fashion, slang, music and deportment - the old sourpuss! And he was only 25 when he wrote this!), some dark and criminal doings, and (sometimes) elements of the supernatural. There's nothing remotely Lovecrafty here, but the tale's done with gusto and it shows Bloch hadn't forgotten ol' Ludvig Prinn.