One of those foreigners, Patrick Henri Devillers, a French architect who had worked for Mr. Bo during his tenure as the mayor of Dalian, arrived in China last week from Cambodia, where he had been arrested at the behest of Beijing. Mr. Devillers, who claims he returned here on his own volition, has told French officials that he is helping in the investigation of Ms. Gu.

The relationship between Mr. Heywood and one of China’s most fabled political families remains murky, the subject of considerable gossip and innuendo. But friends say he met Mr. Bo and Ms. Gu in Dalian in the 1990s and later helped arrange schooling in Britain for the couple’s son. Those with knowledge of the party’s investigation say he was also involved in helping the family transfer illicit funds overseas.

Like her husband, Ms. Gu is the offspring of a revolutionary hero, and like many “princelings” she experienced her share of hardship during the Cultural Revolution. Forced to fend for herself after her family was imprisoned, she worked for a time as a butcher and a bricklayer, according to accounts in the state news media. In the late 1970s, though, she was among the first batch of students to be admitted to college after the death of Mao.

“Courage is more important than wisdom,” she once wrote in a book that detailed her successful pursuit of a case in an American court that yielded a $1 million settlement. The book was something of a sensation and led to the creation of a popular television show whose protagonist — a comely, quick-witted legal crusader — was based on Ms. Gu.

Her legal practice flourished, thanks in part to the connections of her husband, who later became commerce minister.

“They were like royalty in Dalian,” said Edward O. Byrne, an American lawyer who helped Ms. Gu file her 1997 lawsuit in the United States and later spent time with the couple in China. “The people who worked for them would refer to them as the Kennedys of China.”

By most accounts, Ms. Gu was fiercely devoted to Bo Guagua, her only child. In 1998, she accompanied him to Britain, where he attended a private preparatory school, and later, the elite Harrow School, which was Mr. Heywood’s alma mater. According to Mr. Heywood’s friends, he was instrumental in helping the boy gain admission to Harrow, which charges annual tuition equivalent to $55,000. Ms. Gu spent at least two years in Britain, where she went by the name Horus, the Egyptian god of war.