A never-before-seen Christmas guest arrives to the island, filled with secrets of her own. The Sheridans welcome a brand-new baby. Complications arise left and right as the Sheridan sisters grapple with another season of changes.The Sheridan sisters' mother, Anna Sheridan never spoke much about her family, which is why the appearance of her younger sister is a surprise for all of them. She brings with her a host of troubles at the very worst time, as Audrey arrives home from a tumultuous semester at Penn State, just as Christine gives birth to her very first child.Audrey has had a horrendous time away from baby Max. She grapples with guilt for going after her dreams, as she fears missing out on more essential moments in Max's life, and also questions her feelings for the handsome man she met earlier this year, when Max was in the hospital after birth. Romantic love has never been particularly good to her. Why should she trust it, now?Christine faces the biggest mountain of all: motherhood. Is she ready for this stage of her life? She's feels as big as a whale and terrified of making every possible mistake.The Vineyard Christmas guest will prove herself a missing link of their happiness during a strange and overwhelming Christmas time, with all the familiar cast of Sheridan family members: Susan, Christine, and Lola, plus their daughters, partners, father, cousins, and friends.