Dirk Bogarde brings considerable charm to this somewhat silly spy narrative unfolding during the Cold War era. “Whistler,” a writer facing difficulties, unexpectedly receives a job offer through the local employment agency. He finds himself impressed by the luxurious offices of "Cunliffe" (Robert Morley) and his assistant "Allsop" (John Le Mesurier), along with the surprisingly high salary of £40 per week, completely bewildered that they would hire him for a position in an industry he knows nothing about. His initial task involves traveling to Communist Czechoslovakia to meet with another glass engineer; after exchanging prearranged phrases – which gives the film its name – swapping books and returning home directly. It seems straightforward enough, but naturally, it’s more complicated than that. He is unaware that his employer is manipulating him, and that the Czech intelligence service, led by "Simoneva" (Leo McKern), is also aware of his movements. Simoneva even enlists his attractive daughter "Vlasta" (Sylva Koscina) to drive him, intending to quickly capture him—though this plan doesn't proceed as intended either. Eventually realizing the true nature of his situation, our unfortunate “Whistler” must reach the safety of the British embassy before he is discovered having seemingly fallen from a high-class hotel window. The film leans toward slapstick and feels overly written at times, but the talented cast members contribute to an enjoyable atmosphere, with Bogarde’s performance perhaps echoing his work in "Doctor..." films rather than his more serious roles. Nevertheless, viewers familiar with British comedy will recognize many of the actors, and the occasional parody of “James Bond” is hard to miss. It isn't a masterpiece, but it’s worth seeing, I think.

Source on TMDB