Andrea lives with her widowed father, Benigno, and her younger brothers, Damian and Marcelino. Her boyfriend is Jason, a young musician, but she breaks up with him when she discovers that he is involved in illegal activities. Andrea is a bright, decent girl with an outgoing personality and an adventurous streak. She is about to start her freshman year at college, but her dreams are cut short when her father suffers a serious accident that confines him to a wheelchair and sinks him into a deep depression. Andrea, only seventeen, realizes that it’s now up to her to support her family. She looks for a job, but the only well-paid position she can find is in Maximo Arrioja’s law firm, as the personal assistant of his son, Dario. Unfortunately, Dario’s fiancée, Moira, is extremely jealous and cannot stand the idea of a woman working so close to her boyfriend, so the position becomes only available for a young man. 

Coincidentally, it was Dario who rushed Benigno to the hospital when he was run over, and Andrea is very grateful to him. Since the job at the firm calls for a man, Andrea daringly makes up a twin brother, Andres. With the reluctant help of her friend Juan Vicente, who teaches her how to act like a man, she gets the job. Juan Vicente is in love with Andrea, but she sees him as an older brother. Andres soon becomes Dario’s constant companion, since Maximo wants him to find out what his son is up to during the hours he disappears from the office. Andrea eventually discovers his secret but keeps it to herself. Dario owns a multimedia business called Eureka, built up with money given to him by his grandmother, Mercedes. He only studied law to please his father but his real passion is his business. Andrea’s problems start when Dario’s sister, Ximena, meets Andres and falls in love with him. Andrea falls into unique situations trying to avoid her. To make matters worse, Maximo offers her (Andrea) a job and, to increase her income, she accepts. Now she works as Andrea and Andres, and must juggle between both jobs without giving herself away. Each day, Andrea is more attracted to Dario, yet she harbors no hopes since he is engaged to Moira. 

Maximo discovers Dario’s secret company and demands that Mercedes stop supporting him financially. She refuses. Dario, however, takes on the challenge of making it on his own and comes up with a plan to find new talent to promote and turn into a teen idol. By chance, he hears Andres sing and knows he has found his star. Dario breaks up with Moira and confides in Andres that he loves Andrea. Soon after, he and Andrea start dating. She knows she’ll soon have to tell him the truth, but when she is about to do it, Moira—who had discovered her double identity—threatens to expose Andres as a fraud and bring down Dario’s company if she doesn’t break up with him. 

A Double Identity is a riveting story brimming with romance, music, intrigue and youthful exuberance; with intensely dramatic confrontations, highlighted with moments of deep tenderness and humorous mix-ups caused by the best intentions of this adorable young firecracker who will capture the hearts of viewers both young and old.