there will be the devil to pay

There will be a huge amount of trouble (if a particular thing does/does not happen or is/is not done). There'll be the devil to pay if they catch us sneaking out this late at night! If you don't have that report finished by lunch, there will be the devil to pay!

Serious trouble resulting from some action, as in There'll be the devil to pay if you let that dog out. This expression originally referred to trouble resulting from making a bargain with the devil, but later was broadened to apply to any sort of problem. A variant, the devil to pay and no pitch hot, first recorded in 1865, gave rise to the theory that the expression was originally nautical, since pay also means "to waterproof a seam by caulking it with pitch," and no pitch hot meant it was a particularly difficult job, since cold pitch is hard to use. However, the original expression is much older and is the one that survives. [c. 1400]

Serious trouble, a mess. The expression originally referred to making a bargain with the devil, and the payment that eventually would be exacted. It first appeared in print about 1400: “Be it wer be at tome for ay, than her to serve the devil to pay” (Reliquiare Antiquae). This Faustian type of trouble was later lightened to mean any kind of problem (Jonathan Swift, Journal to Stella, 1711: “The Earl of Strafford is to go soon to Holland . . . and then there will be the devil and all to pay”). In the nineteenth century the expression was expanded to “the devil to pay and no pitch hot.” This form referred to “paying,” or caulking, a seam around a ship’s hull very near the waterline; it was called “the devil” because it was so difficult to reach. (See also between the devil and the deep blue sea.) Sir Walter Scott used it in The Pirate (1821): “If they hurt but one hair of Cleveland’s head, there will be the devil to pay and no pitch hot.”