A Trap for a Trader

On a mild, damp March afternoon in 2011, Sarah Tighe and her husband Tom Hayes arrived in the prenatal wing of London's University College Hospital. They were there for Ms. Tighe's 12-week pregnancy scan.

The pregnancy was off to a difficult start. Ms. Tighe had suffered from severe morning sickness. Mr. Hayes, a disheveled, mildly autistic 32-year-old mathematician, hadn't been helping matters. He didn't seem especially concerned with her discomfort. Instead he was preoccupied with his favorite British soccer team, Queen's Park Rangers, and his firing months earlier from Citigroup, which had accused him of trying to manipulate an important interest rate called Libor.

Rebuffed by several other banks where he'd sought jobs, Mr. Hayes was slowly coming to terms with the fact that his career as a wildly successful trader had come to an end. More troubling, he'd heard rumors that governments were investigating his conduct.

As a midwife moved an ultrasound wand over Ms. Tighe's growing midsection, Mr. Hayes's cellphone rang. The call was from a number—and country code—that he didn't recognize. Anxiously lying on an examination table, Ms. Tighe told her husband to ignore the call.