The Girl in the Red Velvet Swing is the true story of Evelyn Nesbit (Dame Joan Collins), a beautiful showgirl caught in a love triangle with elderly architect Stanford White (Ray Milland) and eccentric young millionaire Harry K. Thaw (Farley Granger).

It's the early twentieth century New York City. There exists a high level of animosity by Harry K. Thaw (Farley Granger), a wealthy Pittsburgh businessman, toward renowned architect Stanford White (Ray Milland) for Harry feeling those dealing with the New York City and social set giving Stanford many of the perks that should rightfully have gone to him. While Stanford is mature and refined, Harry is brash, impetuous, and volatile. That animosity is ratcheted up a notch when they both meet Evelyn Nesbit (Dame Joan Collins), a beautiful but poor model with whom they are both infatuated, she appearing in the chorus of her first Broadway musical revue. After getting to know Evelyn, married Stanford, who still loves his wife and thus will not divorce her, wants nonetheless to provide Evelyn with the comforts and breeding of those within his social circle. His infatuation with her is also despite he being old enough to be her father. Harry, who is more age appropriate, takes a more direct approach in his pursuit of Evelyn, he doing whatever to convince her that Stanford is taking advantage of her. Regardless of what the two men do for her, Evelyn admits that she is in love with Stanford, although she is not sure if she can assume the role of the hidden other woman. What happens within this triangle is affected more not by what the two men will do to win Evelyn, but rather the stronger feeling the two men have in not wanting to see Evelyn with the other.—Huggo