Harry England, a British car salesman on a trip to France meets a Baroness when her Rolls-Royce Breaks down. They spend a few days together and become lovers before she disappers one night, but Harry does not know her surname. The Baron then hires Harry to teach his teenage son about cars on their country estate. Harry discovers the Baroness again and their affair continues. Harry falls in love and asks the Baroness to leave the Baron who has taken up with a lady of his own. Hello-Goodbye is a light comedy where one of the funny moments occurs with a drunk Harry driving a prize vintage car into a swimming pool.

Classic car enthusiast Harry England stops his Aston Martin at a filling station on the French Riviera. There he meets Dany, an attractive aristocrat whose Rolls-Royce has broken down. In Paris they visit bistros and spend the night in a cheap hotel. When Dany suggests a visit to Marseilles, Harry insists on a trip to London, and they part company. From Cannes Harry is summoned by the Baron de Choisis and offered a job as caretaker of vintage automobiles and companion to de Choisis' 16-year-old son Raymond. Accepting, Harry discovers that the baron's wife is Dany. With the apparent approval of the baron, the two thereupon resume their affair. After taking an apartment in Marseilles, Harry begs Dany to leave her husband. When she refuses, the mechanic resigns his position, gets drunk, drives the baron's Rolls-Royce into the swimming pool, and departs. Upon later learning that the baron has left his wife for American heiress Evelyn Rosson and that Dany is sailing to America, Harry rushes to the docks of Le Havre, where he persuades the departing Dany to remain with him.