Casey is Helen's older sister. She returns to Nantucket after being abandoned by her husband, Stuart Davenport, but despite having grown up on Nantucket, she has difficulty adjusting her upper crust tastes and sensibilities to a working class life on the small island. Her relationship with Brian cools after that, but they maintain a friendship. When she first appears in the show, Casey goes by her married name of Davenport, but after she and Stuart divorce at the end of season seven, she reverts to Chappel.