Maddy De Costa

 is a character on Treason. She is portrayed by Oona Chaplin.

Biography
Maddy is an ex-army officer who is now an occupational therapist working with veterans.

She is Adam Lawrence's second wife. She is devoted to him and is the stepmother of his two kids, Callum and Ella. Maddy wants answers when Adam's promotion to M16 chief jeopardizes their family, especially after discovering her husband has been in contact with his ex-lover, Kara Yerzova. She begins secretly monitoring Adam after her suspicions are roused.

While in the military, she served alongside Dede Alexander in Afghanistan. When the agency launches an investigation into Maddy's husband, Adam Lawrence, Dede takes on the case to protect Maddy and use her as an asset.

Throughout Treason
When Maddy's daughter, Ella is kidnapped, she worries about the safety of her family. She shares these concerns with her friend in the CIA, Dede Alexander. They previously served in the military together, and Dede had saved Maddy's life. Dede gave Maddy a pen that could record sounds within 10 metres, which she used to record Adam's phone call with Kara. Later, Maddy followed Adam when he met up with Kara, and she took a photo of the two. The recording and the photos were handed to Dede.

Maddy plants a gift card with a tracker in Adam's wallet to help the CIA track him. They follow him when he meets with Kara again. Maddy joins Dede in the van while they track Adam. She overhears Adam's conversation with Kara, where she tells him it was the CIA who kidnapped Adam. Maddy is angry at her friend for betraying her. The two argue outside the van, and are spotted by Adam. Maddy feels betrayed by Dede, as it was the CIA who kidnapped Ella and Dede had been using her to get information. However, Dede told Maddy that Ella was not her daughter by blood.

Appearances

 * Treason

Trivia

 * Maddy says her last name is Spanish, and she speaks Spanish.