It’s about time the South Street Seaport got a speakeasy.

Mr. Cannon — a new cocktail destination that has concocted its name from a fictional, 19th-century drink-mixing prodigy — is opening next month in a dark little space that used to be the back of a retail store at 206 Front St.

If you have trouble finding the joint, look for a door that bears an old-style woodcut portrait of a well-tailored rat. Inside, you’ll find a low-lit, 600-square-foot tavern that seats 25 imbibers who can enjoy the creations of in-house master mixologist Christopher Kearns.