Set in the 1850s, "The Passing of Grandison" opens with the story's unnamed third-person narrator commenting on how Dick Owens, the lazy son of a wealthy Southern slave owner, attempts to impress the woman he is courting. After attending the trial of an Ohio man found guilty of kidnapping a slave from his cruel master, Dick goes to see Charity Lomax. Dick admits he is more sympathetic to the guilty man than he is to the slave owners. Charity considers the Ohio man a hero and says she could never love Dick unless he did something similarly heroic.
The next morning Dick asks his servant, Tom, if he would like to travel north with him for a holiday. Tom is keen to escape, so he agrees, but Dick's father doesn't like the idea of the young slave leaving the plantation and mixing with rascally abolitionists. Instead, he suggests Dick take Grandison, a loyal slave who Colonel Owens considers "abolitionist-proof."
The first stop on the trip up north is New York City. Dick gives Grandison plenty of personal freedom, but to his disappointment he finds the slave waiting for him at the hotel every night. Dick relocates to Boston, where he writes an anonymous letter to local abolitionists, informing them that a cruel slave-master has arrived in Boston with his slave. The abolitionists attempt to sway Grandison to seek freedom, but Grandison rejects their arguments and hopes to return to the plantation soon.
Desperate to get rid of Grandison, Dick takes him to the Canadian side of Niagara Falls, where Grandison is legally free. However, despite having another chance to escape, Grandison stays loyal to his master. Finally, Dick pays a local man to kidnap Grandison.
Before his return to Kentucky, Dick sends a letter to his father informing him about the flight of the slave. The old man is initially enraged as he trusted Grandison, but his rage transforms into annoyance at the abolitionists who took him. When Dick comes home, he recounts the story to Charity, who agrees to be his wife. They are married within weeks.
Three weeks after his abduction, Grandison returns in poor condition. He is wholeheartedly welcomed by the colonel, who can now renew his trust in his slaves. Grandison is set up among the house servants and is allowed to marry Betty, an enslaved maid.
After another three weeks, Colonel Owens wakes up to learn that Grandison and Betty, together with Grandison’s relatives, are gone. He forms a slave-hunting posse with other slaveholders, but they can't quite catch up with the fugitives. The story closes with the colonel glimpsing Grandison and his family on a steamboat on Lake Erie, headed for Canada. He shakes his fist powerlessly as the slaves reach freedom.
