Lydia is a frequent visitor at Mayfield Psychiatric Hospital that soon becomes emotionally attached to Gregory House. She has a husband whose sister is catatonic and hasn't said anything for years that is also at Mayfield. She was portrayed by Franka Potente.
House heard Lydia playing the piano not long after being admitted and was drawn to her while avoiding the other patients and staff. She was playing to Silent Girl(Annie). House asked her how she got the key to the piano; she told him that they gave it to her, and that she visited often to play for her husband's sister as it was the only thing she reacted to in the form of swaying to the music. House informed Lydia that her head was not swaying to the music but to her pulse. A claim he would later take back, admitting that he hummed to Annie while Lydia was away.
House found Lydia playing the piano again and wondered why she still played even though she got no response from Annie. Lydia told House that Annie was a master cellist and loved music before she became catatonic to which he suggested that since she played the cello that maybe Annie would respond better to that. During her next visit to Mayfield, House noticed Lydia unloading a large Cello case, smiling as he realized she had listened to his prior advice, he waits for her to reach his floor and engages her in playful conversation. House convinced Lydia to ask Steve/Freedom Master to help bring the Cello from her car to improve his depressed state. While letting Steve regain his confidence, House asked her if they could go for a drive. While driving, House convinced her to let him borrow her car, technically stealing it. In part to get away from Mayfield as he longed to do, but more importantly to help Steve regain his old identity as Freedom Master, which Lydia recognized as an act of a good heart, implying she trusted House despite barely knowing him.
While initially House's plan was a success, it lead to Steve's delusions getting the better of him causing him to jump off a parking garage resulting in serious injuries. House, caught completely unaware and faced with his guilt over the fact he was to blame for his compromised judgement, relented and started accepting treatment from Dr. Nolan. One of the more significant parts of the therapy was to attend a party at Mayfield intended to push House to reach out to strangers and hopefully show them who he really is. House ran into Lydia while avoiding the party goers, they hit it off as usual. She became a willing accomplice to House's scheme to have fun at the expense of total strangers, pretending to be married and forcing a random woman to admit something she didn't do . As the night died down they sat and began talking again, she confided in him that she only married her husband because she loved his sister, that they were best friends and she missed her deeply, feeling her brother was the only person who could relate to what she was going through at the time. She also helped to ease House's guilt over Freedom Master. As they said good night to each other , Lydia kissed House. House spent the whole day afterwards trying to figure out what the kiss meant. At her next visit to Mayfield he finally asked why she kissed him. To which she replied "How many reasons are there?" She said straightforwardly, that it was because she liked him, that it was a nice way of showing him that as he played the piano and playfully looked at her.
Soon, after confronting the fact that she was married, he questioned her about the improbability of their relationship, he said that if they didn't stop, someone would get hurt, but if they stopped, someone would get hurt. Which Lydia could not find an appropriate answer to, only that it was just two people having fun, that she didn't want to think about anything else. Later that day, House found Lydia crying. He apologized for what he said but Lydia told him that it wasn't because of that, it was because she thought she was pathetic. She brought Annie's cello, as if she would be able to perform in the Mayfield talent show. Seeing an emotionally vulnerable Lydia faced with the hopelessness of her best friend's recovery, House gently coaxed her to her feet. Sharing an emotionally honest and raw moment, he embraced her as they swayed in each others arms for a while. Caught up in the moment and their feelings for each other, they ended up having sex that night, resulting in an uncharacteristically raw and emotionally vulnerable House.
After the Talent show, House finally worked up the courage to apologize to Steve for what he did. After making his peace, he moved his wheelchair towards the orderlies to line up for their medicine. House noticed the catatonic Steve reacting to Annie when they passed by, he returned Annie's music box to her as house had theorized and she said thank you, which was the first thing she had said in years. Lydia would come in later that day, greeted by House who proudly exclaimed he had a surprise for her, leading her into the main room where her friend was playing the Cello for the Mayfield staff and its patients. Lydia could not believe what she was seeing and was overwhelmed with happiness. Not long after, Annie was cleared to leave Mayfield for good, much to House's dismay when he discovers she's being moved to a rehab facility in Arizona, and her family (including Lydia) was moving with her. Dr. Nolan told House the news when he stormed in to protest having only just found out himself. He asked for an overnight pass and went to see Lydia. Lydia told him that her husband was in Arizona a lot for work purposes but they had been anchored in New Jersey due to Annie needing to stay in Mayfield and now that she was better, they were free to leave. House, painfully honest, said he didn't want her to leave, that he didn't want things to change. She just as honestly replied that she did not want to, but she couldn't break up her family just to be with House. Lydia apologized for not giving him a proper goodbye as she caressed his face one last time, saying she thought it ended kind of perfect.
House would later seek Dr. Nolan out. Able to admit that he was lost after their goodbye. To which he points out that he has reason to hope, because he connected with another human being enough to miss them, and was able to face his loss honestly.