Lily's cousin, and a bachelor when the novel begins. He becomes engaged to Gwen Van Osburgh while staying at Bellomont, and it is at their wedding that Lily discovers Percy's engagement to Evie. Lily comments that she and Jack are similar types of people, both "with all sorts of intuitions, sensations and perceptions" that their counterparts, Evie and Percy, "don't even guess the existence of." Jack is also the first member of the social elite to realize the value of Simon Rosedale. When the novel begins, he has already brought Simon to several functions and tried to ingratiate him with the right people – always in return for stock market tips, of course.