How It All Goes Down
Gilead is an epistolary novel—it's one long letter from an old, dying father to his son. That means it doesn't follow a step-by-step plot structure. John Ames, the old guy writing the letter, will begin a story one day, touch on it later, and maybe conclude it eventually.
There are several recurring plotlines, mostly driven by the characters involved. Edward, Ames's brother, goes to Germany to study and comes home an atheist. A young Ames and his father take a trip to Kansas to find the gravesite of his grandfather. Ames's grandfather gets involved with violent abolitionists and the war effort (that's the Civil War) but becomes estranged from his pacifist son in the process. Lila comes to the town of Gilead seeking baptism and marries the much older Ames. She studies the faith so that she can educate their son once Ames has died.
The central plotline of Gilead has to do with the return of Jack Boughton, the troubled but beloved son of Robert Boughton, Ames's best friend. Ames distrusts Jack and doesn't at all like the blossoming friendship between Jack and Lila.
Ames slowly reveals the reason he distrusts Jack. Jack is responsible for the death of a child—his own daughter. He gets an impoverished girl pregnant and then abandons them. Her home life, the furthest thing from baby-proof, proves fatal when a treatable (and preventable) cut becomes infected. Jack was careless and negligent, and a child died as a result. Ames hasn't forgiven him for this.
So when Jack comes home to Gilead and befriends Ames's own wife and son, Ames is suspicious, to say the least. He guesses that Jack plans to court his wife once he himself is six feet under. His fears, however, are ungrounded. Jack, it turns out, has a common-law wife and son—it's an interracial marriage to which her family objects. They want her to marry someone else.
Ames offers Jack what guidance he can, bestows on him a blessing, and accepts him as a "son"—but how much any of this will help Ames never learns. Jack departs Gilead once again, never having told his own father the truth about his life.