Lone, the home secretary, is among Shamsie’s most sophisticated creations. He’s had to thread many needles while rising in British politics. He’s mocked by some for becoming “Mr. British Values. Mr. Strong on Security. Mr. Striding Away from Muslim-ness.”

Shamsie humanizes him. She writes about his “extravagant snort, which his children were always amazed he could restrain from in public life.” The best story told about Lone is probably the one about the time Eamonn was pining over a lost love, a woman his father found diffident. We read about a moment reminiscent of “The Godfather”:

“The door of his bedroom had been kicked open and Karamat Lone had walked in, knees buckling slightly under the weight of the halibut in his arms, ice chips glinting on its skin. He had lowered the massive fish onto his son’s bed, with the single word ‘replacement.’”

Shamsie, who was raised in Karachi, in Pakistan, and lives in London, is vastly better known in England than in the United States. This is her seventh novel. Twice a finalist for the Orange Prize, she was one of Granta’s Best of Young British Novelists in 2013, and writes essays and criticism for The Guardian.

There are occasional small blunders in “Home Fire.” A consideration of grief, for example, becomes a word goop. “Grief spread its wings large like an eagle, grief huddled small like a porcupine,” Shamsie writes, “grief needed company, grief craved solitude; grief wanted to remember, wanted to forget.” Grief wants to be left alone.

These moments are rare. Her humor mixes freely with her intellection. There is a disquisition on “ecosystem beards,” so named because they are so large they contain entire small worlds.

The humor fades into fatalistic meditations on life lived while straddling worlds. Aneeka comes up with a plan to get her brother home, a plan that will have consequences for everyone in this novel.

It’s a plan so intrepid that Aneeka is asked if she or her brother stopped “to think about those of us with passports that look like toilet paper to the rest of the world who spend our whole lives being so careful we don’t give anyone a reason to reject our visa applications? Don’t stand next to this guy, don’t follow that guy on Twitter, don’t download that Noam Chomsky book.”