This is a sad, but well told story—set in Ireland, home of sad stories.  And Donal Ryan knows how to tell them.  The protagonist, Melody, seems evil, involved in a bitter marriage that she ends with pregnancy by her 17-year-old literacy student from a local community of Travellers (Irish Gypsies).  The pace of the novel follows the weeks of pregnancy, each landmark bringing another reason for spite towards her husband, Pat, his family, the village, the Travellers—and her self-hatred. She lives alone in her house; Pat with his menacing family.

Mary, a young Traveller ostracized by her husband Buzzy's clan because she is barren, befriends Melody as she lurks around the camp.  The troubles caused by Mary’s infertility and Melody’s fertility are the soul of All We Shall Know. Melody keeps her pregnancy secret from the young father, using it only to wound her husband and his family.  Mary's family enters into a protracted battle with Buzzy's clan, who claim he was cuckolded.  Melody’s own father, a passive figure, accepts her situation, and provides a safe home and care as the pregnancy ripens.  Unhappy in his marriage to Melody’s deceased mother, you feel he can begin life again with a grandchild.  

Ryan’s writing is flat-out beautiful.  

“I could still fly to London and end this, and come back and say, Yes, Pat, I was
lying, and he could persuade himself to believe me, and we could take a
weekend break somewhere and be massaged together, and walk along a river
hand in hand, and stand beneath a waterfall and feel the spray on our faces and
laugh, and think about the cave behind the falling water, cut off from the world,
and all the roaring peace to be found there, and have a drink in the bar after
dinner, and go to bed, and turn to one another's flesh for warmth, and find only a
hard coldness there, and no accommodation, no forgiveness of sins; and we'd
turn away again from one another, and lie apart facing upwards and send words
into eternity about babies never born, and needs unmet, and prostitutes and
internet sex and terrible unforgivable sins and swirling infinities of blame and
hollow retribution, and we could slow to a stop as the sun crept up, and turn from
each other in familiar exhaustion, and sleep until checking-out time on pillows
wet with tears"

All We Shall Know is concise, 180 pages, and spell-binding.  Highly recommended.