In the basement of the American mission, inside the SCIF, they were looking at the same game. Helen Sykes had a screenshot up on the display. It was a street scene from “Nova City,” where the game’s animated figures, almost lifelike but somehow eerily not, were going about the business of the game. Teenagers smoked joints in front of a bodega. A yuppie couple with a baby stroller hurried down the sidewalk. A gangster in a red Camaro was shooting at a police car.

“This was on a monitor,” she said, “in the room where a Navy SEAL squad sent an Islamic State logistics officer to paradise.”

The FBI man looked at the screen appraisingly. This was something he knew about. “That game’s like a movie,” he said. “Human images, sexy girls. Isn’t that against their religion?”

“We don’t think he was playing,” said Sykes.

“It’s a game,” said the DS man.

Helen Sykes didn’t reply. She just zoomed in past the teenagers, the yuppie family, and the gangster in the Camaro to the wall behind the police car. There was gang graffiti on the wall. “The player in Murder City can spray paint over graffiti,” she said.

“Okay,” said the DS man.

“If the game is hacked,” she said, “the player can use the spray can to write his own messages on the wall.”

Everyone looked hard at the screen. Rafe spoke first:

“So, if someone is online, in multi-player mode . . .”

“Yes,” said Sykes. “Other players, wherever they are in the whole wide world, can read those messages.”

The DS man shook his head. “A fucking computer game? Sending terrorist instructions?”

“Assume NSA is on it,” said the FBI man.

“Hard to keep track of every kid in the world playing a first-person shooter,” said Frank.

“I play that fucking game,” said the FBI man.

“What fun,” said Sykes.

“What’s written on the wall?” asked Rafe. “What messages were posted?”

“I thought no one would ever ask.” Sykes zoomed in tight on the wall, on the messy tags, and she read them out.

“The Latin Dukes want the Eighth Street Crew to fuck their mothers in the ass. Rodney 17 apparently just wants the world to see what a great artist he is. And Mister J,” she said with emphasis, “wants Homeboy to go to Lake City and make a connection before Wednesday.”

“Today’s Wednesday,” said the DS man.

“Well, now we’re making progress,” said Sykes.

“Do we know when that was posted?” asked Rafe.

Sykes shook her head. “It could have been a week ago. It could have been a month ago.”

“Where’s Lake City?” asked the DS man. “Is that a place in the game?”

“No,” said the FBI man, who knew because he played the game.