It's called a Chamber of Reflection. These rooms are designed as cold, austere places in which a Mason can reflect on his own mortality. (219)
This room is Masonic? (219)
Robert Langdon is flown out to Washington D.C. to do a lecture on symbology and mythology at the Capitol for the famous Peter Solomon. But as it turns out, Solomon did not fly him out to Washington. Langdon eventually finds out Solomon is being held hostage at an undisclosed location somewhere within the city. Langdon then finds Solomon's severed hand, marked with various Masonic symbols at the center of the Capitol Rotunda.
Change of plans, take us to Freedom Plaza! (374)
As he was about to walk out, Langdon comes across the CIA and its director and discusses on finding Peter Solomon. With the help of Langdon's knowledge in symbology, he was able to lead the group deep into a labyrinth beneath the Capitol that can potentially lead to the location of Peter Solomon. According to the CIA, Solomon's kidnapper was a "threat to American security."
Suddenly, the Architect of the Capitol, Warren Bellamy, helps Langdon escape the grasp of the CIA and leads him to a separate secret underground chamber. He explains that he has something that needs to be protected at all costs. Then, he reveals a pure gold pyramid, resembling the golden Masonic capstone. On the contrast, the CIA easily tracks down Langdon and Bellamy as they begin to get out of the Capitol building.
During their escape, Bellamy and Langdon contact Katherine Solomon, Peter Solomon's younger sister, an avid researcher in noetic science at the Smithsonian Institute. Since Katherine and Peter were Masons, Katherine was able to help Langdon and Bellamy decipher the capstone in order to get to the location of the pyramid before Peter's kidnapper. Eventually, Bellamy was captured by CIA agents, leaving the job to Langdon and Katherine.
Eventually, Langdon and Katherine were forced to work with the CIA. Their motive was to neutralize Peter Solomon's abductor. The kidnapper's plan was to use Solomon as a sacrifice to the ancient gods. At a moment's notice, the CIA agents raid the abductor's home. The agents fail and the abductor was able to take Langdon and Katherine into his basement, where they were also taken hostage.
Luckily, the CIA was able to bring in backup as the abductor and Solomon escaped. The agents were able to free Katherine and Langdon before they died from their injuries. As the abductor was about to sacrifice Peter Solomon, Katherine, Langdon and the CIA crash into the room. As it turns out, Peter's abductor was actually his son, Zachary Solomon, who supposedly died in prison. Peter was able to free himself as the bullets came raining down on his corrupted son.