Shawn Butler arrived in Port Charles shortly after Molly Lansing had been involved in a bus crash. He found the young girl struggling to deal with the aftermath of the crash. Shawn calmed her and admitted he was a former marine and suffered from something similar called post-traumatic stress disorder (PTSD). A friend of Molly's mother found Shawn and Molly together. The friend was Carly Corinthos Jacks and she thanked Shawn for helping Molly and offered him a complimentary room at her hotel. Shawn declined the offer and explained he was in town to interview for a position at a law firm working as a security consultant and investigator.
The actual job Shawn had arrived in town for was did involve investigation and security but under the guise of employment at a law firm. Theo Hoffman, a powerful crime lord also known as the Balkan, hired Shawn to investigate the death of his son and bring his son's killer to justice. Shawn's first task involved sending a message to Johnny Zacchara by means of a brutal beating, which he carried out according to Theo's orders.
The next task Theo assigned to Shawn was to kidnap Brenda Barrett on the day of her wedding to Sonny Corinthos. Shawn was in position to grab Brenda but Carly interrupted his plans when she paid Brenda a visit prior to the nuptials. Shawn decided to walk away from the mission instead of bringing any harm to Carly. Meanwhile, Jason Morgan discovered that Theo was behind the threats against Brenda and he wanted answers from Shawn.
Jason and Shawn held one another at gunpoint until Shawn admitted his loyalty was to himself and his code of honor, not Theo. He explained that he was a free-lancer and had only recently started to work for Theo and would not harm any women or children, which is why he walked away from the opportunity to kidnap Brenda. Jason and Shawn formed a temporary alliance and agreed to work together to stop Theo. They decided to use Shawn's connection to Theo as a means to lure him to the Pine Barrens. Theo realized it was a set-up and opened fire.
Amidst the chaos of the shoot-out, Shawn disappeared and Jason assumed that Shawn had double-crossed him and had rejoined Theo. Instead, Carly found Shawn passed out on the side of the road with a gunshot wound. She brought him to her house and cared for his wound. Carly also protected Shawn from both Jason and Sonny when they accused him of having a role in planting a car bomb and kidnapping Brenda. Shawn supplied Jason with everything he knew in an attempt to aid Brenda's safe rescue.
The police eventually learned that Shawn had worked for Theo and he was hospitalized for his gunshot wound. During his stay in the hospital, one of Theo's men tried to kill him and he decided to leave the hospital. He made a brief trip out of town to gather his records on Theo and shared everything he found with Jason upon his return. Brenda was found and Jason appreciated all that Shawn had done to help bring her home.
Shawn remained in Port Charles after he gained Jason's trust and was hired by Jason as a bodyguard for Carly and her daughter Josslyn. A reclusive serial killer named Franco had threatened Josslyn while she recovered from a kidney transplant. Josslyn's father Jax and Carly were estranged and in the midst of a heated custody battle. Jax did not approve of Shawn guarding his daughter. Jax offered to pay Shawn to quit but he refused.
Eventually Jax forced Shawn out of Josslyn and Carly's life after he dug into Shawn's past and discovered he had been dishonorably discharged from the military because he had killed a fellow marine. Jax threatened to use Shawn's presence in Carly's life against her in the custody battle. Although Carly defended him, Shawn did not deny what he had done and he quit. Shawn confronted Jax and ordered him to leave Carly out of whatever issue Jax had with him. Jax taunted Shawn and he responded with a punch to Jax's face.
Shawn kept his distance from Carly and Josslyn until the custody battle was over and Jax left town. Carly had been awarded sole custody of Josslyn but Shawn did not believe that Jax would give up his daughter so easily. His instincts were correct and he walked in on Jax as he tried to kidnap Josslyn. Jax brought up the incident in Shawn's past in which he had unintentionally injured a young girl, the same event which had caused the post-traumatic stress disorder. Shawn was flooded with the memories and he temporarily froze while Jax walked away with Josslyn.
After Shawn recovered, he started searching for Josslyn. Shawn knew Jax was unable to drive away with Josslyn because Shawn had tampered with Jax's car earlier. He then made his way to Jax's private jet to ensure Jax was forced to remain in town. When he arrived at the jet, he learned Sonny had already disabled the plane. Shawn knew Jax was most likely on foot and thought about who he would turn to for assistance in fleeing town. He remembered that Jax was good friends with Robin Scorpio-Drake and he made his way to her home.
Shawn was successful in locating Jax and Josslyn and he convinced Jax to allow him to return Josslyn to her mother. Carly was grateful to Shawn and she shared her feelings of remorse over how her marriage to Jax had ended. Shawn decided to remain in Port Charles a bit longer in case Jax returned to take Josslyn again. The reason was moot once Jax's plane went down in the harbor and he was presumed dead. Jax's body was not found and Carly believed Jax might still be alive. Shawn encouraged her to trust her instincts and provided Carly with hope when he reported that Carly's boat was missing from the harbor.
Carly tried to show her appreciation for all Shawn had done by setting Shawn up with a teaching position at Port Charles University and offered him a room at the Metro Court. Shawn declined the offer and decided to rent a room above Kelly's. He also accepted a job working for Jason in the Corinthos organization. The job entailed watching over Sonny and managing the organization while Jason got married and embarked on his honeymoon to Hawaii. He also continued to watch over Carly and her daughter. An attraction brewed between Shawn and Carly but Shawn pulled away and claimed he needed to maintain a professional relationship.
Shawn solidified his position as Jason's right-hand man when he prevented the cops from discovering illegal drugs that had been planted at the warehouse where a police officer had been shot. He constructed a bomb to clear the cops from the warehouse so he would have a chance to move the drugs. Carly arrived as Shawn destroyed the bomb he had made and Carly showed him a panic room where the drugs could temporarily be stored. The door locked behind them and they were briefly trapped together. When the door opened, the cops had returned and accused Shawn of planting the bomb. Carly covered for Shawn and led the cops to believe they were sleeping together and had used the panic room for a romantic tryst.
After their statement had been given, Carly continued the charade that they were lovers in front of her ex-husband Sonny, but Shawn denied that they were involved. He refused to be a pawn in Carly and Sonny's relationship and was flustered when Carly later asked if he found her attractive. He walked away instead of answering her question and assumed she was vying for his attention when she claimed her daughter was in danger.
Carly produced proof that Franco had reached out to Josslyn again in the form of a gift and that Jason needed to be warned. Shawn paid Jason a visit in Hawaii to discuss the possible threat. Against his wishes, Carly and her daughter joined him on the trip. Jason and Shawn were unable to find any proof that Franco was in Hawaii so Shawn, Carly, and Josslyn returned home. Carly and Shawn grew closer in Hawaii but Shawn refused to act on Carly's advances.
Jason returned from his honeymoon, he informed Shawn that Franco was back and instructed Shawn to make protecting Carly and her daughter his top priority. Shawn moved in with Carly so he could guard her and the pair continued their pattern of getting close until Shawn pulled away. They spent Thanksgiving together and shared a romantic dance but Shawn prevented things from going any further. Carly remained frustrated with the distance Shawn insisted remain between them and did not believe his claim that he could not protect her properly if he became too involved. He admitted something could happen between them but he was determined to prevent it.
Shawn remained focused on his work and he attended a meeting in place of Jason. The meeting was an ambush and Jason's associate Bernie was wounded by a gunshot. Shawn handled the situation but was overcome by his post-traumatic stress disorder afterwards. Carly arrived soon after and was concerned over the state of shock she found Shawn in. Carly learned that therapy dogs can help with PTSD and she presented Shawn with a dog for Christmas.
Although Shawn was no longer assigned to guard Carly, he was concerned about her involvement with Johnny Zacchara. However, Shawn's focus shifted when a teenager named T.J. arrived in Port Charles and took up residence with him. T.J. was the son of the man that Shawn had accidentally killed during his time in the Marines. Shawn felt guilty about the position he had placed T.J. and his mother in and he agreed to care for T.J..
Since Shawn was inexperienced in parenting a teenager, he turned to Carly and Alexis Davis for advice. They helped him enroll T.J. in a private school and Alexis offered to have her daughter Molly tutor T.J.. Carly and Alexis also helped Shawn out after T.J. stole a car and tried to pose as a staff member at Carly's hotel.
Shawn was concerned about T.J.'s interest in a career in the mob after he learned that Shawn worked for Sonny Corinthos. This prompted him to take a position at Port Charles University as an academic counselor. Carly's son Michael was assigned to work with him and Shawn decided to reconsider pursuing a relationship with Carly. He asked her to attend a benefit with him at the Metro Court but she did not respond to his offer. When chaos ensued at the benefit, Shawn was concerned after he saw Carly take off after Johnny. However, he had to deal with the underage drinking party T.J. held at Molly's home before he could track down Carly.
After T.J. and Shawn discussed the party, T.J. accused Shawn of never going after what he wanted. T.J. used Shawn's feelings for Carly as an example. After the conversation, Shawn decided to speak with Carly and he found her at Johnny's penthouse. Shawn asked her to be with him instead of Johnny because he believed they could be good together. Carly declined and decided to pursue a relationship with Johnny instead. Shawn was disappointed was Carly's decision to be with Johnny but they remained friends.
Although T.J.'s advice regarding Carly did not work out the way Shawn had hoped, T.J.'s relationship with Molly did and the teens started dating. When Molly's mother Alexis Davis learned that they were together she demanded that they stop seeing one another immediately. Shawn intervened on behalf of T.J. and Molly and convinced Alexis to allow them to date under supervision. Alexis agreed and Shawn started spending more time with her.
Around the same time, Shawn was involved with a woman named Rosie but he started to develop feelings for Alexis. The pair bonded during a game of strip pool and Shawn started to think about Alexis romantically. He ended his relationship with Rosie but feared he had lost his chance with Alexis after she and Carly's daughter Josslyn were both injected with a mysterious substance that caused them to run a dangerously high fever. Shawn waited at the hospital and prayed for both Alexis and Josslyn. When he learned that they were going to survive, he approached Alexis and asked her out on a date.
Alexis agreed to go out with Shawn but Jerry Jacks returned to Port Charles and delayed their date. He poisoned the town's water supply and everyone except Josslyn and Alexis had been exposed to the deadly toxin. Shawn and T.J. spent what they believed were their final hours with Molly and Alexis at their home. Jerry showed up and took Alexis as his hostage after an altercation with Shawn.
Shawn managed to track down Jerry and Alexis despite the effects of the toxin and he rescued Alexis. Afterwards the antidote to the toxin was given and Shawn made a full recovery. He and Alexis continued to spend time together and he was her date to Sonny's wedding.
Shortly after Alexis and Shawn entered into a relationship, Jason was shot and presumed dead. Shawn decided to help fill-in for Jason within Sonny's organization from time to time, much to the dismay of Alexis. She admitted that she cared for Shawn and would be devastated if any harm were to come to him. Shawn returned the sediments and they became lovers.
Alexis and Shawn continued to grow closer and Alexis helped care for Shawn after he was shot in the park. He had been doing surveillance work per Sonny's request after Lulu Spencer had been kidnapped. Shawn was speaking with the police when a gunman approached. Shawn moved to protect the police commissioner Anna Devane after a bullet was fired and he was shot in the process. He recovered in time to escort Alexis to the Nurse's Ball.
Shawn's relationship with Alexis was tested after Franco was revealed to be alive and Sonny and Carly ordered him to kill Franco. At Carly's insistence, Shawn complied with the request, unaware that Sonny had called off the hit. However, Olivia Falconeri walked in the path of the bullet meant for Franco and she was shot instead. Although Shawn tried to cover the truth, Alexis suspected that Shawn had been involved in the shooting.