This is an in-universe article with out-of-universe material.
Jimmy Olsen bought the apartment and hoped that it could be a place where he and Chloe Sullivan could start their lives together once they were married. However, after the events of their terrible wedding, followed by their separation, Jimmy decided to keep it a secret.
At the end of season eight Jimmy brought Chloe and Davis Bloome to the Watchtower on Clark Kents request to keep them safe and then there, he confessed to her that it was her wedding present and that he was going to give it to her after the reception. After Jimmy revealed to her that he knew Clark's secret, she apologized about everything she did. After Jimmy told her that he understood, they proclaimed their love for each other and reaffirmed their relationship. Then, an angry Davis murdered Jimmy by stabbing a pole through his chest. He was enraged at Chloe about the lies that she told him, and was about to kill her too, but Jimmy stepped in using the last of his strength and pushed Davis into a spike, killing him. Jimmy told Chloe that he loved her and then he died in her arms.After Jimmy's funeral, Clark went to the tower to visit Chloe. After talking with her, he suggested that Chloe should leave the apartment and walk away. Chloe refused the idea, and insisted that Jimmy is still there and is watching over her. Then she revealed that she plans to use the building as a base, a Watchtower like her codename, to bring the heroes together after Oliver Queen and his team leave the town. Clark told her that heroes don't have homes and that Clark Kent was now dead before walking away, leaving Chloe alone in the building.
Chloe took refuge at the Watchtower after the death of Jimmy and sat alone for 3 weeks trying to find Lois Lane, who had been missing. When she heard a noise in the hallway, Chloe grabbed her gun and went to investigate only to find Emil Hamilton who was looking for her. Chloe explained that she couldn't find Oliver or any of the other Leaguers and Emil was shown to be skeptical to the idea of Chloe arguing that not one of them wanted to be found. After a touching and optimistic speech of Chloe's, Emil provided the Watchtower with lots of high tech computers and then Chloe thanked him. Using the new technology at her disposal, Chloe found that her cousin had definitely been in the future.
When Lois was kidnapped by John Corben Clark went to Chloe's Watchtower looking for help. Chloe used the computers to locate the building which could be hosting Corben. Once Clark saved Lois, he returned to the Watchtower and saw the whole city from the stained glass window. He said that Jimmy had done well to choose the site and then apologized to Chloe for leaving her when she needed him. Chloe admitted that she missed Jimmy and then also apologized to Clark for thinking that he had gone ahead without looking back. After an emotional moment, they reconciled their friendship and then Chloe advised Clark to return to his double life at the Daily Planet to protect Lois from Tess Mercer.
Chloe used the tower to watch their teammates, and above all to observe Oliver as he was the most difficult to locate. When an airborne virus was released in the air from one of the Kryptonians, Chloe worked with Clark and Dr. Hamilton to find a cure. From the Watchtower, Chloe was able to infiltrate the security cameras of the Luthor Mansion to find out what was happening and when Clark brought a blood sample from Tess Mercer with which the virus could be analyzed in detail, she and Hamilton managed to use the medical laboratory located in the tower to remove a blood sample from Clark and make a cure.
When the Toyman reappeared, Chloe tracked him down with the tower and along with Clark, delivered him to the police. Later, Chloe used the computers to investigate a mysterious woman who had kidnapped Oliver and had looted his bank account. She also discovered that several Kryptonians had landed on the planet and managed to locate the exact places where they had appeared.
Trying to locate the Kryptonians, Chloe wanted to hack into the computer networks of Tess's to look into her projects in order to find something but was constantly neutralized by the firewall of the system. After an arduous battle, and after one hundred disabled firewalls, Chloe eventually managed to find her adversary and using a modern system of fingerprint detection, was able to get the files of her opponent. Later, people like the Dark Archer or Sylvester Pemberton found out about Watchtower and more recently the government agency Checkmate wanted to know where its location was. Chloe upgraded Watchtower's system because, of these threats.
Soon, Tess Mercer broke into Watchtower and triggered an alarm that shut down the doors that trapped both Chloe and Tess in the building. Chloe discovered that Tess had a bug in her body and that Checkmate was closing in their location in order to kill them. They thought they were done for and Tess confessed that Oliver was lucky to have someone like Chloe and then Chloe found out how to escape, but at the cost of shutting down Watchtower. They are able to bust the metal doors of Watchtower but it shut down as a result.
Chloe was later able to repair most of Watchtower and was afraid at first, until Clark convinced her that the world needed her to do this and that he needed her to do this. This convinced her to activate Watchtower again and open the doors.
Later, when the Kandorians started to attack the planet, the heroes gathered where Clark told them that he planned to use the Book of Rao to exile all the Kandorians to a new world where they won't be a threat to anyone and that he would be forced to join them as a result of this action. They tried to make Clark reconsider but he told them that this was the only way to settle the matter without going into war and losing lives. The heroes said their goodbyes to Clark and signed off.
The Kandorians cut off communications from Watchtower, so Oliver prepared to leave in order to get the connection back up with Watchtower via a satellie that Chloe was unaware of and they shared a passionate kiss before he departed. Chloe was navigating Oliver through the ventilation shafts in order to get to the connection up. He succeeds but then Chloe detects many others surrounding Oliver and started to attack the shafts, putting dents. They proclaim their love for each other and Oliver told Chloe that they weren't Kandorians before the line went dead.
- Chloe's job as super-hero information broker as well as living in a tower-base in the center of the city is an obvious homage to Barbara Gordon, who as Oracle plays the same role, and who also lived in a tower in the center of Gotham City.
- It is never revealed how Jimmy, being a modestly employed photographer, was able to buy what must have been a hugely expensive penthouse apartment in a building which dwarfs even the LuthorCorp building. It is possible Oliver Queen could have helped Jimmy pay for it or may have bought it himself for Jimmy.
- The new Watchtower Satelite that Oliver mentions in Salvation, has an association with the actual Satilite Watchtower that appears in the comics, which is also the team's centeral headquarters.