The story begins when Lyra Belacqua—an orphaned, eleven-year-old girl residing at Jordan College, Oxford—secretly enters the Retiring Room, despite resistance from her dæmon, Pantalaimon; an animal-formed, shape-shifting manifestation of her soul. Inside the room, they see the Master of Jordan College attempt to poison Lord Asriel, Lyra's uncle. Lord Asriel shows the resident scholars a picture of mysterious elementary particles called Dust. Shortly afterwards Lord Asriel goes north, and Lyra continues with her normal life.
However, before long her friend Roger is kidnapped by "the Gobblers", who are the subject of a children's superstition. Lyra vows to rescue him, and finds her chance when a visiting woman of great importance, Mrs. Marisa Coulter, offers to take Lyra away from Jordan College to become her apprentice. Lyra assents, but before she leaves is entrusted with a priceless object by the Master of the College: an alethiometer. Resembling a golden compass, it is a device able to reveal the answer to any question asked by the user. Although initially unable to read or understand its complex meanings, Lyra takes it with her to Mrs Coulter's flat. Lyra becomes suspicious of Mrs. Coulter's motives when Mrs Coulter's dæmon searches Lyra's room for the alethiometer.
At a party hosted by Mrs. Coulter, Lyra discovers that Mrs. Coulter is the head of an organization known as the "General Oblation Board" and that this board is, in fact, the "Gobblers" who have been kidnapping children. The horror of this discovery causes Lyra to take advantage of the hubbub of the party to flee Mrs. Coulter's flat.
After fleeing the flat she is rescued by the gyptians, a group of nomadic, canal-boat-dwelling people, who afterwards reveal that Lord Asriel and Mrs. Coulter are none other than Lyra's father and mother. She also learns that many children like Roger have been disappearing from among the gyptians, and that the gyptians are planning an expedition to the north to rescue the missing children. During her time with the gyptians, Lyra intuitively learns how to operate the alethiometer.
Lyra joins the expedition to the north, and on the journey discovers that the children kidnapped by “the Gobblers” are having their dæmons cut away from them, by way of experiment. Shortly after this revelation, the group is attacked, and Lyra is taken to the experimentation facility in Bolvangar.
Inside it, she locates Roger and builds up a plan of escape. Lyra comes across Mrs. Coulter, who tries to take the alethiometer from her. Narrowly escaping her clutches once again, Lyra leads the other children out of the facility, and is rescued by Lee Scoresby (an aeronaut who is an ally of the gyptians) in his hot air balloon. With them go Roger and an armoured bear called Iorek Byrnison. Iorek is an exiled prince of the armoured bears, of whose culture he is a perfect example.
Now Lyra has found Roger, she wishes to deliver the alethiometer to Lord Asriel, who is imprisoned at Svalbard, the fortress of the armoured bears, because of his experiments on Dust, which the Church opposes. On their way to Svalbard the balloon is attacked by the batlike cliff-ghasts; Lyra is thrown out, but lands safely. She is then captured by the armoured bears. She manages to trick the usurping bear-king, Iofur Raknison, into allowing Iorek Byrnison to fight to regain his throne. Thereafter she travels to Lord Asriel’s cabin, accompanied by both Iorek and Roger.
Despite being imprisoned, Lord Asriel is so influential that he has managed to accumulate the necessary equipment to continue his experiments on Dust. After explaining the nature of Dust, which is an emanation from another world, and the existence of parallel universes to Lyra, he departs, taking Roger and a great deal of scientific equipment. Lyra pursues him, but Roger is killed when he is severed from his dæmon (by falling down a cliff while Lord Asriel's dæmon is holding Roger's). This act releases an enormous amount of energy, which, due to Lord Asriel’s equipment, tears a hole through the sky into a parallel world. Lord Asriel walks through into the new world; on the advice of Pantalaimon, Lyra decides to follow him.
(from
Wikipedia.org)