It's been 4 months since Beckett last saw Castle in precinct. First two-three months after her self-imposed exile from the loft in particular and her husband's life in general Castle was being Castle. He constantly wormed himself into 12th precinct's investigations, finding every possible and impossible way to be near her, to find answers as to why she left him and make her come back. He was not as helpful, as usual in breaking the cases though. Beckett knew that it was because his mind was not really much into the mysteries themselves. He was focused instead on finding the answers to her unexpected behavior – she indeed left him right after they told each other not to hold anymore secrets and went on the justice quest to bring down the Locksat, mysterious organization, that was behind murder of her former team at AG office and she felt herself compelled to bring justice for them and didn't think that anybody other could or would do it. At first, Castle was even able to garner some help from Esposito, Ryan and Lanie in keeping him in the loop of the ongoing cases and Beckett's whereabouts during some of them. It was both cute and heartbreaking at the same time, to see him doing all the funny, clumsy and stupid tricks to make her see that they are always better, when they are together; but it was making everything for her harder. She didn't like being away from him any more, than he did. She just couldn't tell him anything about Locksat, because he would, undoubtedly, want to help her, protect her, and it could get himself and his family in danger and it was the last thing that Beckett wanted for her husband, stepdaughter and mother-in-law. She couldn't also just drop the investigation, because that's not how she was built. Her sharp sense of justice, her desire to find the truth and make the perpetrators pay for their deeds, inability to give up, when everybody else has already left the wagon wouldn't let her stay in peace. Castle himself called her extraordinary on numerous occasions for these same qualities. Sure he would understand, once she will be able to tell him everything after the end of her investigation. It won't be easy and it won't be quick, but Beckett hasn't held any doubt that eventually Castle will forgive her and take back once the truth will be disclosed.
But, with Castle regularly in the precinct she couldn't focus on her off-page investigation. She feared that he could get a hold of it, if he was near while she investigated. Besides, she missed him as well and seeing him, but not being able to give a way to her feelings and needs was taking a toll on her. She also had to run interference several times between Castle and Vikram. It looked, that Castle suspected him in having a hand in Beckett's removal from his life, so he couldn't bear seeing Vikram with Beckett and was constantly trying to get a ruse from the newly accepted tech assistant of the 12th precinct. It didn't help, that Espo and Ryan also didn't like Vikram and were covertly taking Castle's side in those disagreements. So, at some point she told them in a no nonsense way, that they are helping nobody in letting Castle to the precinct and their cases and that she will transfer them to some tedious and unpleasant arrangements, if they would continue doing it. She was crossing some lines there and power abuse was definitely present in her orders, but she couldn't find any other ways to accomplish her mission, if Castle still was present at the precinct. Detectives were not happy with her and that conversation brought some tension between them and Beckett, but it was far better, that dealing with Castle. From that day Castle was slowly been pushed to the curb by all of them. Of course, he didn't give up easily, he continued to show up on occasions. Beckett knew, that he tried to talk and even bribe a bit the Detectives and the medical examiner; fortunately, they didn't bend, fearing Beckett's wrath and thinking, that Castle might have done something wrong, thus deserving such an attitude from their Captain.
Castle still resisted several weeks more, but his visits and calls became less and less regular, until he finally quit. Beckett couldn't pinpoint the exact moment he stopped, but she was relieved, when a week passed with no call or visits from her husband. She got engrossed in her investigation, simultaneously running the precinct with no side distractions. After a month she run out of clothes and needed to visit the loft to pick more of her stuff. When she called Castle to ask, if she can stop by to replenish her wardrobe, Castle was cordial, if a little distant. When she knocked the door of the loft at the arranged time, nobody opened, so she used her own key. The loft was empty and it was a little disconcerting. She quickly took everything she needed, including one of the Castle shirts and leaving one of her own for him, just as she did it the last time.
During next several weeks there were still no communication from Castle and she started to worry. Beckett began to peruse social media and newspapers' 6th pages to see, if she can find anything relating to Castle that might help her understand, if there is something going on with her husband. Surprisingly she came out empty, as there weren't any mentions about Castle. It was a little strange, because even after their marriage Castle was quite a regular guest of galas, charities and events, which were held in NY almost every day. It's funny, she thought, how she did everything to push him away to be able to focus on her investigation and now, when she got what she wanted, she hoped that he would disobey her, as per usual and would start annoying her by trying to reach out to her. She waited a bit more, so her excuse of running out of clothes wouldn't get old or suspicious and called her husband again for the second time in three months. Again, as the last time, Castle was quite forthcoming and assured her, that she is welcome to come and pick up everything she needed. That day Beckett went to the loft two hours earlier that they agreed, hoping to catch Castle home and she was quite disappointed to find the loft empty again. She couldn't figure out, if Alexis and Martha weren't eager to see her on their own or that was Castle's doing and he had asked them to leave the loft for the time of her visit. She still wanted to leave him one of her shirts, when she noticed, that the shirt she has left the last time was laid on her side of the bed, just as she left it, quite visibly untouched. It was painful to see, that Castle didn't need or didn't want to find solace in her scent, while she was away and unavailable, as she did during all these nights alone in a bed in some second level motel.
This finding, along with another dead end in her investigation with Vikram on mysterious Locksat operation started weighing hard on her. She couldn't bring herself to invest fully in the investigation. Restrained relations with Espo and Ryan weren't helping the matter as well. She couldn't turn to her dad, because she couldn't see the way to explain everything to him and not telling anything about her off the book activities.
With the Thanksgiving Day approaching, Beckett hoped that she would receive an invitation from her husband to a feast dinner which was a must thing in the Castle household. There was no way that Castles would skip such an important celebration which Rick, usually, started to plan in October. Alarmingly, that day came and passed with no calls from any member of her family and she had to celebrate it in the precinct with Vikram and on duty officers with frozen turkey sandwiches from the nearest supermarket. Not bothering about the excuse anymore, she called Castle the next day to check how he was doing and whether they were celebrating Thanksgiving without her. Castle calmly told her, that neither he nor Martha or Alexis wanted anything big this year, so they just drove to Hamptons and had a dinner in their beach house with no guests, just the three of them. When Beckett asked, if everything was fine with him, Castle said, that he is doing OK and that he is pretty busy with writing and his PI business. Except the occasional "how are you" Castle hasn't asked anything else about Beckett and her intention to come home anytime soon. Not knowing what else to ask without starting a serious conversation over the phone Beckett ended the call, wishing her husband good luck.
Now, 6 months from the day she walked out on Castle and 4 months from the day she has last seen him in person, on the day of the first anniversary of their wedding, with no invitation from Rick to celebrate it, she stood before the door of their loft, desperately wanting to find out what's going on with her husband and with intention to mend their relationship, before it would be too late and irreversible. She knocked on the door, but the loud music coming from the loft made it clear, that it was impossible for anybody inside to hear the knock, so she used her key and entered the loft.