Liam and Callie's relationship started 2-3 years prior to the Pilot episode. It was revealed by Callie that Liam had started to act nice towards her and they soon began a relationship. After some time, however, he snuck into her room late one night where he asked Callie if she wanted to have sex. When she declined, explaining that she wasn't ready, Liam raped her. After this, Liam claimed to their foster parents that Callie came onto him which resulted in Jude and Callie being forced out of the home. Callie felt immense guilt for this, since the home had been the best one they had ever been to (until the Fosters) and believed nothing would have happened if she just kept her distance from Liam.
When Callie met another teenager, Sarah, whom is living with the Olmsteads, she is threatened by Liam who saw her at Wyatt's party in Saturday, to stay away from her. However, Callie still tried to warn Sarah about Liam, only to be rebuffed when Sarah said Liam already told her about her and that she is just jealous and crazy. He escalated Callie's terror by stalking her, making it clear that he knew where she lived. Wyatt later sends an online threat to Liam which lead to Liam to visit Callie's school to further harrass her. He pulled on her wrist with aggressive force again threatening if she didn't stay out of his business.
Before he could further harm her, Wyatt tackled him to the ground. They started a physical altercation until Brandon, who was walking home, noticed the fight and ran over to stop them. Liam leaves after Callie demands he go away. Later on, Callie confides in Brandon about her story with Liam and how he attacked her and while she initially felt guilty for her rape, she eventually realized that despite her relationship with Liam at the time, it wasn't her fault.
It is revealed that Liam has been grooming Sarah and planned to attack her as well. She drags Liam to court taunting him with "You know what you did to me." Liam won the case due to insufficient evidence of the rape. Since Callie has told Stef and Lena about the incident, a police report was filed as well as the removal of Sarah from the Olmsteads home, ensuring her safety from Liam.
In season 2, in Truth Be Told, Liam still haunts Callie. While thinking she was ready to have sex with Wyatt, Callie started hallucinating Liam. It is later revealed she is still dealing with her rape.
In Leaky Faucets, Wyatt and Callie go to a Mexican carnival. However, Wyatt spots Liam at the carnival and breaks his promise of staying with Callie when she needed him. Wyatt told Brandon about Liam and started looking for him. They confront Liam and he taunts them that Callie wanted it. Wyatt, angered, punches Liam. Liam retaliates by punching him back. Brandon tries to stop the fight however he is hit in the nose and participates in the fight. Wyatt holds Liam in retaliation and Brandon begins to throw blows. The police eventually interfere and stop the fight. Liam decides not to press charges and leaves after seeing Callie.
In Not That Kind of Girl, Callie was revealed that she has major debts to owe to the bank. Callie denies her involvement and accuses fraud with the purchases consisting of purses and so on. While working at the drop-in center, she spots Sarah with an expensive purse. Stef goes behind the background and discovers that Liam is illegally selling purses to women who want it. She sets up an undercover operation as a woman interested in buying one. She meets with Liam at an enclosed location and buys the purse. She asks him if she remembers him. When he replies that he doesn't, he reveals her real identity and police badge and tells him he is arrested. Liam tries to run away but is caught by Mike who was back up. Liam is in the interrogation room. Callie asks that she break him down. Stef, initially worried, reluctantly agrees. Callie tells him about the rape investigation. She reveals to him about the purses and committed fraud and tells him that she finally caught him. It is presumed that Liam later incarcerated for his crimes.
- Callie and Liam are seen talking about Sarah.
- Callie and Liam are seen talking to Wyatt.
- Callie and Liam are seen arguing outside of school.
- Callie and Liam are in court for his rape of her.
- Callie and Liam briefly see each other.