Maytime in Mayfair is concerned with England's high-fashion set, especially those creatures whose designs set the tone for London's upper crust. Two of the leading emporia are located directly across the street from each other, one run by the lovely Eileen Grahame (Anna Neagle) and the other by the charming but scheming D'Arcy Davenport (Peter Graves). Davenport feels threatened by Eileen and would like nothing more than for her to close up her shop. One day, a young man by the name of Michael Gore-Brown (Michael Wilding) appears. As appealing as he is in debt, it turns out that he has fortuitously inherited the shop for which Eileen designs. Although encouraged to sell it immediately and get some desperately needed ready cash, he becomes quite taken with Eileen and decides to hold on to the salon. At the same time, D'Arcy manages to get his hands on Eileen's latest, top-secret designs and disseminates them to the press, which will ruin Eileen. Thinking that it is Michael that has done this terrible deed, Eileen leaves and goes to Paris. Depressed that his true love has spurned him, Michael is all set to sell the business to two buyers (who are secretly acting on D'Arcy's behalf) when Eileen returns, having discovered the truth.