fall for something hook, line and sinker

fall for something hook, line and sinker

or

swallow something hook, line and sinker

If someone falls for something hook, line, and sinker or swallows something hook, line and sinker, they believe it completely, even though it is often not true. He told her a story about having lost his money, and she fell for it, hook, line and sinker. There were leaks to the press, and journalists swallowed it hook, line and sinker.
See also: and, fall, line, sinker, something