A Brooklyn single with a ticking biological clock (Greta Gerwig) decides to conceive by artificial insemination, but the pregnancy is complicated by her unexpected love affair with a married man (Ethan Hawke). Writer-director Rebecca Miller (The Ballad of Jack and Rose) gives Gerwig a more appealing character than the glamorous snots she often plays, and her early scenes with Hawke, doing his usual shaggy comedy, are charming. But the story grows emotionally muddled after Miller (adapting a story by Karen Rinaldi) leaps ahead three years: now the two lovers are unhappily married parents, and the Gerwig character, for motives unclear to us and possibly herself, contrives to reunite her husband with his ex-wife, a dour academic (Julianne Moore). With Bill Hader, Maya Rudolph, Wallace Shawn, and a musical cameo by riot grrrl Kathleen Hanna.