Casey Chapel

Played by Amy Yasbeck, Casey is Helen's older sister. She returns to Nantucket after being abandoned by her husband, Stuart Davenport (played by John Ritter, who was Yasbeck's real life partner and later husband), but despite having grown up there she has difficulty adjusting her upper crust tastes and sensibilities to a working class life on the small island. Antonio falls madly in love with Casey, but she takes little notice of him.

After she and Brian spend the better part of a season sniping at each other, they end up having sex the night before Joe and Helen's wedding. Afterward they find themselves unable to stay away from each other, having a passionate affair; while Joe and Helen are on their honeymoon, Casey's bra lands on the hearth of the lit fireplace and leads to Helen's house burning down. 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.