The Subtle Knife, sequel to the luminous, entrancing The Golden Compass, opens in our own universe. Will Parry, 12, has killed a man, and he's now on the run. Granted, the man was searching his house at the time, and Will was only trying to get away, but the horrible memory clings to him. With his father, an explorer, long since disappeared, and a mentally unstable, paranoid mother, Will is far older and wiser than his years, but by the time he gets to Oxford, he's unnerved and exhausted. That's when he sees what appears to be a door cut into the air.

Will watches a cat disappear through the doorway, and he follows the cat into another world, an apparently deserted city by the sea. There he encounters a girl about his own age, Lyra, heroine of The Golden Compass. They learn that they are in Ci'gazze, in a world linking Will's world with Lyra's, where adults are in hiding from the Specters that sap their souls.

Will and Lyra go back into Oxford, and Lyra learns that there are physicists who are doing research which corresponds to some of the studies going on in her own world. But the scientist she talks to turns out not to be an ally, and in running away, Lyra inadvertently runs to another enemy, who steals the aletheometer. Will and Lyra confront the man, who says he will return the aletheometer if they bring him a knife -- the subtle knife -- which cuts the doors and windows between worlds. Lyra and Will return to Ci'gazze and find the knife. They also find that it is inextricably linked to Will's destiny.

Intertwined in the story are elements from the previous novel, such as the ongoing search for Lyra and Lord Asriel's struggle to complete his work. In addition, Will continues the quest for his father.

The second book in the His Dark Materials trilogy, The Subtle Knife holds up well. Fully understanding the complex plot is dependent on reading the first book; Pullman does an excellent job of filling details without being too expository, but certainly a level of emotional involvement is lost if one has not read The Golden Compass. Will is a strong, resolute and wholly likable character, but Lyra is somewhat less appealing. This could be because one sees her from an outside point of view, but neither is she entirely unappealing.

Many middle novels in a trilogy serve merely as little more than a bridge between the development of the first novel and the climax in the third. The Subtle Knife tells its own story with fervor and integrity, from the suspenseful beginning to the stunning -- and shocking -- end.