Harvey's Fiancee (S03E04)

At the hunt ball, Baines encounters a friend named Lucy Maitland. With his mother scheduled to visit before heading to his sister's place, Jane disguises herself as Lucy to distract Baines' mother from Harvey's new fiancée. Meanwhile, Tom and Diana hilariously impersonate Baines' parents while interacting with “Lucy.” Their antics successfully convince Lucy to leave, allowing Jane to reclaim Baines all to herself.