Thomas Kilbride, the young man at the center of Linwood Barclay’s delightful new novel, spends up to 16 hours a day at his computer. Mostly, he’s at the Whirl360 website, where he can explore almost every street in most of the world’s cities. He memorizes countless details about many thousands of streets because he believes a calamity — a terrorist attack, an earthquake, even an alien invasion — will destroy all the world’s maps. Then he will save America with his unique ability to tell the CIA how to move its agents from one location to another. Thomas frequently sends emails to update the CIA about his plans.

A complication arrives with the death of Thomas’ father, who has been caring for his son at his farmhouse in upstate New York. Thomas’ brother, Ray, a freelance cartoonist, must decide what to do about his younger brother. Ray thinks Thomas should be in a supervised group home, but Thomas resists. Then, while exploring a street in Greenwich Village at his computer, Thomas sees a woman’s face at a window and thinks she’s being murdered. Ray suggests it might be some sort of dummy with a wig. Thomas says that if Ray won’t go investigate, he’ll walk to New York himself. Ray reluctantly makes the trip.

Barclay also introduces Morris Sawchuck, New York’s attorney general, who wants to run for governor and then for president; and Howard Talliman, his all-around fixer. They, too, have a problem: Morris’ sexy young wife, his third, is being blackmailed, and the blackmailer may know things that would block the road to the White House.

Soon a lot is happening. We readers have begun to fear that Thomas might have been involved in his father’s supposedly accidental death. There are hints of a traumatic event in Thomas’ life when he was 13 that he refuses to talk about. And one day two unsmiling FBI agents show up at the door to see if he might be some sort of terrorist. (When they leave, Thomas comments, “I thought they were nice, but they should have sent the CIA.”)

Barclay’s story is expertly plotted, and he moves easily between sweetly comic scenes and entirely sinister ones. When Barclay presents his unsentimental portraits of killers and politicians, he recalls Ed McBain at his most mordant. It’s a nice balancing act.

Delusions are far from unknown in literature. You can go back to Uncle Teddy in Arsenic and Old Lace, who thought he was Teddy Roosevelt and was forever charging up San Juan Hill, or to Elwood P. Dowd, in Harvey, whose constant companion was a 6-foot-3 1/2-inch rabbit that only he could see. We’ve had less of that kind of humor lately, perhaps because political correctness discourages writing that might be seen as poking fun at the mentally challenged. As if we all weren’t mentally challenged and frequently delusional.

Patrick Anderson reviewed this book for The Washington Post.