When does Olive Kitteridge return?

The HBO miniseries is based on Elizabeth Strout's 2008 novel. It stars Frances McDormand as Olive Kitteridge, Richard Jenkins as her loving husband Henry, Zoe Kazan as Denise Thibodeau, and Bill Murray as Jack Kennison. The show is divided into 4 parts, each depicting a certain point of time in the novel.
Olive Kitteridge is a misanthropic and strict, but well-meaning, retired schoolteacher who lives in the fictional seaside town of Crosby, Maine. For 25 years, Olive has experienced problems of depression, bereavement, jealousy and friction with family members and friends.