The house has a portico at the front and a large foyer. To the right of the foyer is a drawing room, to the left a library. Beyond the foyer is a hall leading to the kitchens and other servants rooms.
Given the period and style, it's likely that the house is 4-5 stories, with bedrooms on the upper floors and servants' rooms toward the back of the house.
After returning from Ardsmuir Prison, Lord John begins staying with his mother at the house in Jermyn Street.
Lord John is still living primarily at Jermyn Street, along with his mother and his cousin Olivia. After a long day, Lord John is dismayed to find his mother holding one of her weekly musicales in the drawing room. He is later brought to the house to recover after being poisoned by Joseph Trevelyan.
Benedicta continues to occupy the house in Jermyn Street, with John staying at the house in between military postings. With her husband in the colonies, a now heavily pregnant Olivia has returned to stay at the house as well.
Benedicta elects to keep the house in Jermyn Street even after her marriage to Sir George Stanley, and Hal and Lord John are relieved to learn that Sir George is emphatically in favor of this decision.
William references an orrery formerly belonging to Gerard Grey in the library of Jermyn Street.
The house is located in a highly fashionable part of central London, with St. James's Square to the south and Piccadilly road to the north. However, despite the central location, the street is a narrow and secluded one.