"Romancing Mr. Bridgerton" is the fourth book in the Bridgerton series by Julia Quinn. It centers around Penelope Featherington and Colin Bridgerton. Penelope has harbored a secret love for Colin for years, but she believes he will never see her as more than a friend. Colin, known for his charm and wit, starts to see Penelope in a new light when he returns from his travels. As they grow closer, secrets from the past are revealed, including the true identity of the mysterious gossip columnist, Lady Whistledown. The novel explores themes of love, identity, and societal expectations in Regency-era England.