The most succinct summary of the action in the The Pilgrim's Progress is probably the extended title of the work: The Pilgrim's Progress from this World to That Which is to Come: Delivered under the Similitude of a Dream.
In the first part of Pilgrim's Progress, Christian recieves his calling from the Evangelist and leaves his wife and children behind in the City of Destruction. He effectively maneuvers his way through the Slough of Despond, passes under the Wicket Gate (the gate through which the elect must pass, beginning their journey to Heaven) and soon comes to the Interpreter's House, where he learns to think metaphorically. After leaving this enlightening place, Christian sheds his burden and receives the garb and certificate of the elect from some angels. His next stop is the Beautiful Palace.
After leaving the palace, Christian slips down into the Valley of Humiliation, where he battles and defeats Apollyon, the notorious fiend. After transversing the Valley of the Shadow of Death in the dark, he catches up to his friend Faithful. Christian and Faithful arrive in Vanity-Fair together, where they are arrested under the false charge of inciting a riot. Faithful is tried and burnt at the stake, even though Christian is miraculously delivered. Hopeful, inspired by Faithful's faith, becomes Christian's new traveling companion.
The pair of pilgrims soon come to the Doubting Castle, owned by the Giant Despair, who traps them inside and intends to kill them. Fortunately, their faith allows them to escape from the dungeon and make their way to the Delectable Mountains. The shepherds in the foothills warn Christian and Hopeful about the Flatterer and other potential threats in the last leg of their journey. Unfortunately, the Flatterer manages to fool Christian and Hopeful anyway. An angel rescues them, but punishes them for being so blind when they had been warned. In the final stretch of the journey, they encounter Ignorance, who has not entered the path through the Wicket Gate.
In Beulah, which abuts heaven, Christian and Hopeful arrive at the river. To cross the river is to die, but the must cross it in order to enter into heaven. When they arrive at the gates to the Celestial City, they are welcomed graciously with a trumpet fanfares, and they take their place alongside the rest of the elect. Ignorance gets to the gate, but because he doesn't have a certificate of election, he is sent to hell. The pilgrim's progress to heaven completed, the author awakes from his dream.
Part two begins with Christian's wife, Christiana's, conversion experience, which includes a divine dream and a messenger from heaven. She, her four sons, and her pious young neighbor, Mercy, set out on a pilgrimage, following in Christian's footsteps. Mercy is almost not let through the Wicket Gate, but Christiana intercedes on her behalf, and the pilgrims set out. At the Interpreter's House, they are meet a guide, Mr. Great-Heart, who will lead them on their journey. The pilgrims arrive soon after at the Beautiful Palace, where they stay and study for quite some time. Matthew gets sick from eating the devil's fruit, but he soon recovers. When they finally continue, Great-Heart is there to protect them. They pass through the Valley of Humiliation and the Valley of the Shadow of Death without incident. At the end of the valley, Great-Heart slays the Maul, a giant.
The pilgrims meet Honesty along the road, and he joins their band. Tired, Christiana wishes for an inn, and one appears. The pilgrims stay with Gaius, the innkeeper, for quite some time. Matthew and Mercy get married, as do James and Giaus's daughter. Gaius is a kind and educated man, and a gracious host. After leaving Gaius' place with their new traveling companions, Great-Heart slays another giant, rescues Feeble-Mind, and the pilgrims arrive in Vanity. They stay with one of the few good men in town, Mr. Mnason, and set off again without incident. Great-Heart and the other men slay Giant Despair when they come to the by-path, and they rescue his prisoner, Mr. Despondency.
The pilgrims continue through Madam Bubble's Enchanted Ground, acquring more pilgrims as they go. Soon, they make it to the Delectable Mountains, where the shepherds prepare them for the final stage of their journey. They cross into Beulah and prepare to cross the river. Christiana is summoned first, followed by the rest of the men they picked up along the way. When they have entered triumphally into the City of Zion, the boys (Christian and Christiana's sons) and their wives decide to stay behind to grow the church on earth.