It was a middle-C type note to go out on. The Day The Hot Line Got Hot is a comic spoof on spy films that doesn't quite get off the ground. Someone for some nefarious reasons of their own splices into the famous telephone hot line between the White House and the Kremlin set up during the Kennedy presidency so that JFK and Khrushchev could talk one and one so that there would be no nuclear wars set off by accident. If you remember the hot line figured very prominently in a failed attempt to prevent nuclear war in Failsafe.
Anyway the individual who taps into the hot-line sent messages to both the US president and the Soviet premier that were the equivalent of an international Bronx cheer. They then kidnap the operator forced to send said messages and ship Marie Dubois to Barcelona in one of those old style steamer trunks.
Where things begin to go wrong as the trunks get mixed up and doesn't tourist George Chakiris get a big surprise when instead of his clothing, Dubois tumbles out. Now it's a case of saving the plan which was put in motion for a most interesting reason.
Taylor may have been in the first stages of the cancer that eventually killed him. Charles Boyer has the look of a man waiting for his paycheck to clear, both of them took these roles on possibly for a nice vacation in Spain where the story was filmed. There are a lot interesting jokes about spy training and double and triple agents, in fact that's the key to the whole story.
In any event fans of Taylor and Boyer should see this others will be disappointed.