Intrigue and Inheritance by Catherine Bilson

Just as Elizabeth and Darcy have finally found their footing as a married couple, Lady Catherine de Bourgh arrives unannounced at their London residence with an unexpected demand: they must launch her daughter Anne, along with Georgiana and Kitty Bennet, into London society. Before Elizabeth can protest, Lady Catherine abandons Anne and her companion Mrs. Jenkinson at Darcy House, leaving Elizabeth to navigate the treacherous waters of the ton with three very different young ladies under her care.
As the London Season unfolds, each young woman attracts distinctive suitors. The reserved Anne finds herself caught between the calculating Marquess of Byerly and the poetry-obsessed Lord Joseph Sturt. Georgiana forms a musical connection with the perfectionist Mr. Townend, while Kitty unexpectedly captivates the dramatic Viscount Shandly. Elizabeth and Darcy watch carefully, determined to protect the young women from fortune-hunters and broken hearts.

Their carefully managed Season descends into chaos when a guest collapses at a musicale in Darcy House, dying from poison within minutes. As suspicion falls upon the household, the Darcy reputation hangs in the balance. When a second victim succumbs to the same poison, the evidence points to someone intimately connected to the family. With two murders under their roof, Darcy and Elizabeth must untangle a web of jealousy and obsession before the killer strikes again.