It's Word War I and things are not so quiet on the Eastern Front. Things have, however, apparently quieted down for novelist/soldier Edgar Brodie, as the film begins with his funeral.   Not to worry, though, for the demise of Brodie is just a sham devised so that our hero can be given a new name --Richard Ashenden (played by John Gielgud)-- and sent off to ferret out and assassinate the German spy who has been causing trouble in the Middle East, buying off the Arab tribes.

          A British officer known only as "R" gives Ashenden his new name and assignment then introduces him to a professional assassin (played --to the hilt, one might say-- by Peter Lorre) who calls himself a Mexican and prefers the title "General", even though he is neither.  "R" then sends Ashenden off to Switzerland where the German spy is known to be operating.  Once in Switzerland Ashenden is to join forces with the General and yet another British operative who's identity will be disclosed upon Ashenden's arrival.

          Ashenden checks into the Swiss hotel that will serve as his base of operations only to find that his "wife" has preceded him.  He hustles up to the assigned room to discover the beautiful, blonde Madeline Carroll (as Elsa) half-dressed in the bathroom whilst a young American playboy (Robert Young as Robert Marvin) cools his heels just outside the bathroom door.   [Young seems to have stepped right out of a Hollywood screwball comedy with his formal attire and wisecracking manner!]   Ashenden ushers Marvin out of the hotel room, though not out of the story --Marvin remains always close at hand, shamelessly pitching woo to Esla (who Marvin knows as Mrs. Ashenden) at every opportunity.

          [Another brief aside: in one of the most shamefully over-acted scenes in the film the General, who fancies himself something of a lady killer, throws a fit when he discovers that Elsa has been "issued" to Ashenden in order to complete his cover.  Why, the General demands to know, hasn't he been issued a woman?  The little man threatens to resign, then runs absolutely amok, knocking toiletry off the bathroom shelves, wreaking havoc on a roll of toilet paper. (Oh, the humanity!)]

           The final piece of the setup is Elsa's declaration to Ashenden that she's joined the operation strictly in search of a thrill.

          All right, so everyone's in place and it's just a matter of identifying and killing the German spy.  The one person who might have knowledge of the spy's identity turns up strangled, slouched over a pipe-organ in a small Alpine church, the weight of his body on the keyboard "playing" an unvarying, meaningless set of notes.  However, at the church Ashenden and the General find a clue which, some time later, seems to point directly to an elderly British man (Percy Marmont) staying at the hotel with his little dog and his German (!) wife (Florence Kahn).

          Ashenden and the General con the man into making a trek with them up a nearby mountain, where the "job" can be made to look like an unfortunate accident.  Along the way up the mountain Ashenden has second thoughts about cold-blooded murder and retreats to an observatory to watch via telescope as the General finishes things off. Meanwhile, back at the hotel, Elsa keeps an eye on the German wife, sitting in the woman's room, pretending to take a German lesson --oh, and the persistent Marvin is also there, pitching woo as usual.

          Hitchcock creates tension by cross-cutting between the aforementioned locales and then adds the somewhat sadistic touch of the elderly couple's little dog turning neurotic in the hotel room until it finally lets out a gut-wrenching howl of despair, as if it knows what has just happened to its master.  A close-up of the German wife's face shows she suspects the worst.  Elsa, of course, knows exactly what has happened, and the gruesome scene is enough to turn her off the spy game then and there.

          The three British agents meet that night in a public place, with only the General in a festive mood.  Then comes the message from "R" which decodes (essentially): "the man you mentioned [the one who has just been killed!] is definitely not the man you after".  Ashenden and Elsa go off alone together and reveal their feelings about the whole sordid affair and their feeling toward each other.  They agree to quit the spy game, and fall in love.

          The next morning, just as Ashenden has finished writing the shared letter of resignation, in comes the General with a sure lead to the real German spy.  Duty overcomes Ashenden and he goes off with the General, over Elsa's objections, to pursue the lead.

          I will say only that the remainder of the film involves a spectacular chase through a chocolate factory, a spectacular revelation and, finally, a spectacular train wreck.

          P.s. The acting is top-rate except, perhaps, for Peter Lorre trying a bit too hard to be "colorful".