When had she begun to suspect that her second-floor tenant, Mr. Han, was building a bomb? The idea had come to her slowly, the way she’d ­intuited her husband’s illness in its early days, ­before the lapses and the wandering and the loss of language made it clear to everyone. One afternoon, maybe a month ago, a package from a company called Spectro had appeared in the entryway. 

Mrs. Virag recognized the name from her work. She’d been a chemist for the City of New York, one of the pioneers of a new water-purification system that had lowered dioxin levels by 60 percent. Spectro was a chemical supplier. She picked up the package, thinking it must be for her—she’d received a promotional desk clock from this company just a year ago—but the name on the address label was her tenant’s. The box contained something of ­unusual density. A warning sticker on its side showed liquid dripping from a test tube onto a hand; where the liquid hit, the hand was missing a half circle. 

Soon after that, there were visitors at night—two or three men walking the floor above, arguing at top volume in a language she couldn’t understand. Then, days later, a series of small ill-wrapped packages from China. And last week she’d tripped over a scrap of seven-eighths-inch metal tubing in the hallway. That was when she’d started keeping a list. And the list kept growing. This morning she’d been washing the breakfast dishes when the smell of molten solder dawned over the kitchen. She turned off the faucet and inhaled. There it was, the acrid sweetness of hot lead, the smell that had drifted across Budapest in waves after the war, as the city dug itself out and pieced itself back together. She opened the window and looked out into the street. All quiet. Parents led children by the hand to school; a parking cop changed the roll of his ticket printer. The mayor’s daughter, Chiara, walked arm in arm with a friend; both wore thigh-length flowered skirts despite the cold. No sign of alarm, though there might have been: for the third winter in a row, the neighborhood’s manhole covers had been blowing sky-high at random. Snowmelt and salt had corroded the wires that ran beneath the city streets, according to the papers. Electric sparks ignited pockets of flammable gas underground, and the gas exploded with enormous force. Last week, a man had been walking his dog on the path beside the park when a cover blew and felled him. The man, a father of two, was still alive, hanging on at Methodist in critical condition. The dog had disappeared. Someone had posted signs around the neighborhood—a photo of a sporty-looking Labrador and the plea FIND ABBY!—then, a few days later, exchanged them for new signs with a higher reward.