Then it wasn’t Sam at all. Just a young teen girl, coltish, fourteen maybe. Her parents emerged into the street and went off with her. Sam as a girl. Sam as he remembered her.

He shook his head at his sentimentality, at his evolution into an old man, searching for a girl that wasn’t his daughter, but was as near to that as he’d ever come. Then he went back to his walking.

Everywhere he went, Nakamura sprinkled smart dust. The micro-scale sensors dropped to the ground, spread on the wind, attached themselves to clothing, to shoes, to bags. And everywhere they went, they searched for Kade’s face, for Sam’s face, for a hint of either’s DNA, for the telltale emanations of Nexus. And then they meshed together, each quietly sending data to its closest neighbors, piggybacking until it eventually found its way to Kevin Nakamura.

He swam in that information, overlaid on his vision by his retinal display. Maps showed him the spread of the smart dust as it rode on bellhops and hotel guests to the upper floors of the Hilton and the Sheraton, as it blew through the mall at the heart of Saigon Square, as it was blown or washed into the river and the sewers beneath the city, as it was tracked by bicycles and shoes into the alleys of the maze around Bến Thành Market. A running stream showed face after face after face, flickering by, hundreds of faces so far, none noted as a high probability hit. Further to the side, another stream, of gene sequences this time, just as devoid of true hits.

A layer of the map showed him the Nexus emanations. The area around Bến Thành was inundated with it. Even a few of the less drug-soaked tourists near Saigon Square and the business travelers in the heart of downtown gave off Nexus frequency transmissions. Nakamura shook his head at their audacity, surprised at the prevalence of the drug.

A final map layer showed him police and emergency services data for the city, mined from CIA systems. If the prey can’t be found, he’d taught his pupils, hunt the hunters.

There was always the risk that Sam and Kade would move on, of course. He kept a National Reconnaissance Office AI busy, searching for more matches on that twenty year-old Tata jeep. It threw some at him every few hours, but all were false hits.

He’d love to point a dedicated NRO bird at Saigon. But queries were one thing, retargeting birds was another. The latter would alert the National Reconnaissance Office that CIA had a high level of interest in Saigon. And that was a no-no.

Why? he wondered again. Why so much secrecy?