ON THE EVENING of May 10, Jane Unger made a reconnaissance of her target, on the pretext of buying heroin. She spent half an hour in line outside the clinic with desolate, wheezing Yankees from over the border. The customers lined outside the clinic were the seediest, creepiest, most desperate people she’d ever seen who were not actual criminals. Jane was familiar with the look of actual criminals, because the vast network of former Texas prisons had been emptied of felons and retrofitted as medical quarantine centers and emergency weather shelters. The former inhabitants of the Texan gulag, the actual criminals, were confined by software nowadays. Convicted criminals, in their tamper-proof parole cuffs, couldn’t make it down to Nuevo Laredo, because they’d be marooned on the far side of the Rio Grande by their government tracking software. Nobody in the clinic line wore a parole cuff. But they were clearly the kind of people who had many good friends wearing them.