open-and-shut

open and shut

Clear-cut or straightforward, as of a legal case. Often hyphenated if used before a noun. With all the evidence against the defendant, I expect this to be an open-and-shut case. Her signature on the documents proves she accepted the payment, so it seems pretty open and shut who is responsible.
See also: and, open, shut
Farlex Dictionary of Idioms.

open-and-shut

(of a case or argument) admitting no doubt or dispute; straightforward and conclusive.
Farlex Partner Idioms Dictionary
See also:
  • first hand
  • round robin
  • a round robin
  • eleventh hour
  • heads I win, tails you lose
  • black market
  • a light touch
  • wiggy
  • rust bucket
  • naughty but nice