A Worthy Exploration of War’s Mental Wounds--Take 2 : THE EYE IN THE DOOR <i> by Pat Barker</i> ; Dutton; $20.95, 280 pages

Charles Manning, posted to the Ministry of Munitions in London during World War I in the wake of a front-line injury, is talking to his Army psychiatrist, Dr. William Rivers.

Manning begins by describing how he had to shoot one of his men, Scudder, after Scudder had become trapped in a mud-filled shell hole, sinking slowly and vocally to his death. Reporting to battalion headquarters with another serviceman, Hines, the following night, Manning found his superiors extremely unhappy; dining on veal and ham and wine, the officers informed Manning that he had positioned his company too far forward, creating a bulge in the line.

Manning suddenly realized that he and Hines wouldn’t be offered even a drink. “So I leant across the table,” Manning says, “took two glasses, gave one to Hines and said, ‘Gentlemen, the King.’ And of course they all had to struggle to their feet.” Manning and Hines made a quick retreat, “giggling like a pair of schoolboys,” before the startled brass “could work out how to put an officer on a charge for proposing the loyal toast.”

That’s when the shell hit, Manning says, pointing to his mangled leg. “Poor old Hines. . . . I crawled across to him. And he looked straight at me and said, ‘I’m all right, Mum.’ And died.’ ”

In “The Eye in the Door,” Pat Barker continues the story started in her highly acclaimed novel “Regeneration,” which centered on the conflict encountered by Rivers in his treatment of wounded, often shellshocked infantrymen, notably the soldier-poet Siegfried Sassoon.

As a doctor and a human being, Rivers wanted to make his patients better, whole; but as a British citizen and Army employee, he knew that every medical success meant sending one more soldier back to the battlefield.

Rivers’ internal conflict does play a role in “The Eye in the Door,” but in this novel Barker focuses less on Rivers than on Billy Prior, an angry, shellshocked patient from “Regeneration.” It’s through Prior that we meet Manning, whom Prior picks up for a sexual encounter, and begin to see that the new novel is not only about inwardly divided minds but about the stress triggered by war in society at large.

Prior, like Manning, works for the Ministry of Munitions, but he has a much bigger chip on his shoulder about the war effort. Manning seems to have made his peace with the irrationality of war, perhaps because he still believes in what River calls, in another context, a “terminal stiff upper lip.”

Prior, by contrast, seethes with a barely suppressed rage, caused not by shellshock but the inequitable divisions in British society. And as it happens, at the ministry he can do something about it: A childhood friend, a shopkeeper named Beattie Roper, has been sent to prison for threatening to kill Prime Minister David Lloyd George.

Prior visits her in prison and is quickly convinced that she has been railroaded; a pacifist from the lower classes who freely admits to hiding conscientious objectors, she was an easy mark.

That’s one major thread in “The Eye in the Door.” Another is the real-life libel trial brought against a London newspaper for publishing articles alleging the existence of a German Black Book purportedly giving the names of 47,000 English sexual deviants, many of them in high places.

No matter that the Black Book’s promoter, Harold Spencer, was later judged insane; a similar view is expressed by Prior’s boss, Major Lode, when he says Britain was being “brought to its knees . . . not by Germany, but by an unholy alliance of socialists, sodomites and shop stewards.” Prior can’t tell Lode, of course, that both he and Manning are bisexual, nor that Lode’s obsession with sexual and social distinctions is part of Britain’s problem.

The third major strand in “The Eye in the Door” is Prior’s fugue states in which he commits out-of-character and sometimes violent acts that his conscious mind cannot remember. This Jekyll-and-Hyde theme carries the novel’s weight, because one of Barker’s themes is that authentic feeling, socially acceptable or not, will inevitably work its way to the surface and may well become dangerous if repressed.

Rivers frequently expresses that same concern: It’s better to hate war even as you do the soldier’s job, he tells his patients, than to bury one’s disgust at needless bloodshed and wade through the killing fields like an automaton.

As Rivers muses, after seeing Sassoon again upon the writer’s return to England with a minor head wound:

“Perhaps, contrary to what was usually supposed, duality was the stable state; the attempt at integration, dangerous.”

Passages like that make “The Eye in the Door” an exceptional novel, bringing substantial and relevant ideas to life through singular, arresting characters.

Rivers is the psychiatrist of one’s dreams, willing to change places with a patient if he believes it will do the patient good; Prior is the friend you couldn’t keep, unpredictable and angry enough to keep most acquaintances at a distance.

The novel has its flaws--Beattie’s story simply peters out, for example, and Sassoon’s reappearance seems unnecessary--but it is a worthy sequel nonetheless and a fine achievement in its own right.