“Sisters,” the old Irving Berlin song, winkingly covers primal themes of romance and family; this novel tackles them with detail and realism.

Samantha’s husband, Richard, a highly successful businessman in Boston, cannot stand her sister, Elizabeth, and is only slightly more tolerant of everyone else in their close-knit family. For years, Samantha has felt the strain of this rift, and divorce seems imminent. Then Elizabeth is diagnosed with stage 4 cancer. Samantha devotes herself to her sister’s care and puts her marriage on ice for the duration. While the marriage is the frame, most of the novel concerns Samantha’s experience accompanying her sister to the treatments that extend her life for a few years and supporting her and her family. Privileged with wealth and whiteness, all the characters spend time at elegant restaurants and in luxurious vacation spots; these are the only lighter moments of the book, though the tone throughout is measured, as if appearances weigh on Samantha even as a narrator. Still, she manages to convey the inner torture she feels over her husband’s treatment of her family and then over her sister’s demise. One thread of the novel is troubling, though as realistic as the rest: Richard’s tantrums about Samantha’s family and demands that she choose him over them are textbook emotional abuse. Both spouses eventually work on revising their relationship, going out casually and vacationing together, but Samantha confesses to the reader that it’s like she has “marital PTSD.” She’s not wrong. These are the choices many women are faced with.

In addition to the questions of marriage, this is a portrait of late-stage cancer that makes quietly clear how precious any extra time with a loved one can be.