Oscar and Peter are two architects who run their own company, but they struggle to get the big break they need to become successful. One day, they meet the wealthy businessman Charles Newman, who wants to commission them to design a cultural center in Chicago. However, Newman believes that Oscar is gay and assumes that he will have a more sophisticated understanding of what women want in a building.
To test Oscar's skills, Newman asks him to keep an eye on his girlfriend and personal assistant, Amy. Oscar reluctantly agrees, even though he is attracted to her from the start. As he spends more time with her, Oscar falls deeply in love with Amy and she begins to reciprocate his feelings. However, Oscar is torn between his loyalty to Newman and his growing love for Amy.
Meanwhile, Peter is also dealing with his own problems. He is struggling with his insecurities and jealousy over Oscar's apparent closeness to Amy. He begins to suspect that Oscar is gay after seeing him dressed in drag at a party for Newman. Peter confronts Oscar, and they have a heated argument, which threatens to ruin their friendship and business partnership.
As the competition for the design of the cultural center heats up, Oscar and Peter must put their differences aside and collaborate on a winning proposal. In the end, they manage to impress Newman with their innovative design, and he awards them the contract. Oscar finally confesses his love to Amy, and she reciprocates. They kiss in front of a cheering crowd as Peter looks on with a smile, happy for his friend's happiness.
Overall, Three to Tango is a romantic comedy with a lot of heart. It deals with themes of friendship, love, loyalty, and deception in a lighthearted and entertaining way. The film is elevated by the performances of its talented cast, which includes Matthew Perry, Neve Campbell, Dylan McDermott, and Oliver Platt.