It's the cynicism and the cruelty at the heart of this story that has made its unravelling so compelling - even for a country all too used to horrifying tales of child abduction and trafficking.

As head obstetrician at Fuping County maternity hospital, in Shaanxi province, Zhang Suxia held a position of utmost trust.

New parents, often of first and only children, looked to her for guidance and medical expertise.

Instead Zhang, 56, is alleged systematically to have stolen and sold newborn babies in a string of crimes stretching back eight years.

Her method is now becoming clear, repeated in accounts by family after family. Fifty-five couples have now come forward with similar allegations.

Zhang would tell parents that their newborns suffered from congenital deformities, perhaps on the verge of death, that medical care would be ruinously expensive. For a small fee, 15 dollars or so, she could arrange for them to be taken away, or their bodies disposed of.

In fact, these children were perfectly healthy. The real money was to be made by smuggling them out of the hospital and selling them to child traffickers.

We spent Saturday in Xue Zhen village, waiting for two such children to be returned home.

The twin daughters, born on May 31 to Qi Kuenfeng and Wang Yanyan, had been separated.

One of them was bought for $7,500 by a woman in Shandong province who had been told she had been given up by a young unmarried mother

Choreographed moment

In the event, seemingly unsettled by the media presence, local officials announced that the reunion would instead take place in the county hospital, next door to the building from which the babies had been stolen.

The parents were brought into a crowded, noisy room, with an official shouting instructions.

Mrs Wang clung to her husband, barely able to stand as what should have been a deeply personal moment was chaotically choreographed for the cameras. Not a proud moment for any of us in that room.

But then the tiny girls were brought in by police, and handed to the couple. Both seemed to draw strength from embracing their daughters.

Two little lives that - from their first moments had been nothing but commodities to be traded - now back with their mother and father.

What would Mr Qi tell them when they were older, we asked.

"I never want them to know of this," he replied. "I'm afraid such memories would cast a dark shadow over their lives."

'I feel shame'

Dr Zhang was exposed by Mr Qi's village neighbour, Lai Guofeng. His wife Dong Shanshan gave birth to a son in July.

The obstetrician told the couple that the boy was severely deformed as a result of his mother's syphilis and hepatitis.

In the following days, the family grew suspicious.

Mrs Dong was tested at another hospital and found to be negative for both diseases. They demanded action.

When Mr Lai threatened to jump to his death from a rooftop, police and officials began to investigate in earnest.

Their son was found and returned. But with so many other alleged cases stretching years into the past, these two reunions will be rarities.

And it's no coincidence that the two families live doors apart in the same village.

In a still more cynical twist, it's emerging that Dr Zhang targeted parents that she and her family had had long associations with.

People were more likely to trust her, to believe that she was acting in their interests.

Public crackdown

There are no official statistics for child abduction in China. The best estimates run into the tens of thousands every year.

National government has been engaged in a public crackdown since 2009, and thousands of children have been rescued in televised raids.

But many more parents complain at best of police indifference to their missing children reports.

At worst of complicity among corrupt local officials.

For Qi Kuenfeng and Wang Yanyan, at least, there is a second chance to raise their daughters.

We suggested they would be proud of their parents, for fighting so hard to win them back.

But it's the day he was convinced to give them up that still plays on Mr Qi's mind.

"No. I feel shame," he said. "I feel shame."