The Silver Chair is part of The Chronicles of Narnia, a series of seven fantasy novels written by C. S. Lewis. It was the fourth book published and is the sixth book chronologically. It is the first book, and one of two books in the series, in which the Pevensie children do not appear (the other being The Magician's Nephew).
The book is dedicated to Nicholas Hardie, the son of Lewis's fellow Inkling Colin Hardie.
Jill and Eustace journey toward the far north of Narnia with a gloomy but stalwart Marsh-wiggle, appropriately named Puddleglum. The three cross the River Shribble, which marks the boundary between Narnia proper and the lands of the giants. The first giants they encounter do not notice them (fortunately), but are playing: they are throwing huge boulders at a rock-cairn near the trio. Escaping from these giants, they continue north to a deep and sinister canyon. The sole route across this barrier is an enormous sinister bridge, many times larger in scale than anything a human being might normally use.
After they cross the bridge, hungry and suffering from exposure, they meet The Lady of the Green Kirtle, who encourages them to proceed northward to Harfang, a castle belonging to the "Gentle Giants". Jill, Eustace and Puddleglum are given a warm welcome by the giants, who are in active preparation for Harfang's "Autumn Feast". Refreshed by a sleep in shelter, they look out the window and see the words "Under Me", which they recognize as Aslan's third Sign. Upon discovering that the giants are planning to eat them for the Autumn Feast, Scrubb, Pole, and Puddleglum escape from the castle, force themselves into a small nearby cave and slide down a long dark slope to the Underland They are in darkness, battered and bruised, but they have at least, now followed the Sign that said "Under Me".
They are taken captive by gnomes, placed on a boat and rowed for uncounted days across a "Sunless Sea" to the city ruled by the Lady of the Green Kirtle and a young man being raised by the Lady as a protegé. The young unnamed man treats the travellers pleasantly but does not seem to be right in the head; he himself explains that he suffers from nightly psychotic episodes. During these episodes he must, by the Lady's orders, be bound to a silver chair; if he is released, he will kill everyone within sight, and turn into a green serpent, deadly to all nearby. The threesome determine to witness the youth in his torment, which they sense could be a key to their quest.
As Pole, Scrubb, and Puddleglum witness the young man tied to his chair, his "ravings" seem to indicate desperate health within an enchanted captivity. Finally, after launching a battery of dire threats, the youth begs his companions to release him in the name of Aslan. Recognizing the fourth Sign, they do so. Far from killing them and turning into a serpent, the young man thanks them and reveals himself to be the vanished Prince Rilian, kept underground by the Lady of the Green Kirtle for sinister purposes. Rilian hacks the silver chair to pieces, but the lady returns and tries to bewitch them all into forgetting who they are and where they are from. The barefoot Puddleglum stamps out the enchantress's magical fire and breaks her spell. The enraged Lady transforms into a green serpent, and Rilian realizes that he has been enslaved for all these years by his mother's murderer. Rilian kills the serpent, and leads the travellers in their escape from the Underworld. One of the gnomes, who were also magically enslaved by the Lady and are now freed by her death, discloses that they have been kidnapped from their home even deeper in earth, a land named Bism. The gnome shows the the party a route upward out of the Underworld, before returning to his native land below. Rilian returns to Cair Paravel as King Caspian returns home and meets his long-lost son just before dying.
Aslan appears and congratulates Eustace and Jill on achieving their goal, then returns them to his country at the stream where Jill first met Aslan. The body of King Caspian appears in the stream and Aslan instructs Eustace to run a thorn into the lion's paw. Eustace obeys, and Aslan's blood flows over the dead King, who is revived and returned to youth. Aslan explains that when Jill and Eustace return to their own world, Caspian will go with them briefly, to help set things right there. At the portal between the worlds, Aslan roars, and part of the wall surrounding Experiment House collapses. Caspian, Eustace and Jill cross the wall and give the school bullies, who have gathered at the wall to seek out the two children (no time passes in their own world while the children are in Narnia), a well-deserved thrashing. The beaten bullies run back towards the school in terror, having also seen Aslan. In the confusion Eustace and Jill sneak back into the school building and change into their school clothes while Aslan and Caspian return to Aslan's country.
It is suggested, for example by A. N. Wilson, that the White Witch represents, among other things, modern philosophy in general, with its freezing effect on the religious and mythical imagination being embodied in her "Great Winter". If so, the Lady of the Green Kirtle presumably represents the Freudian world view, with its tendency to explain away all strongly held beliefs as infantile neuroses. Underland would then be the world of the unconscious, and the Silver Chair itself would be the psychoanalyst's couch. (The same two enemies appear as the characters of "old Mr Enlightenment" and "Sigismund Enlightenment" in The Pilgrim's Regress.) This theme is further extended in the book by the mention of the 'Experiment House'(Jill, and Eustace's school) whose main principles seem to be influenced by the philosophy of the psychoanalyst, bullies not being punished but meerly viewed as 'interesting psychological cases'.
The significant part of the story underground also parallels the Platonic Parable of the Cave, which is paraphrased in the sequence where the Lady of the Green Kirtle tries to convince the children, Puddleglum and Rilian that there is no world outside her cave. Puddleglum admits that this is possible, but argues that even if the outside world is an illusion, reality contains nothing of comparable value.
Due to biblical metaphors by Lewis the two northern witches can be interpreted as the devil. A common theme is their pursuit of acts against Narnia, which is Aslan's land. The imagery of the serpent can also be linked to the serpent that tempted Eve in the Garden of Eden.