The phone call came on Friday afternoon.  My colleague took the call.  I could hear his end of the conversation.
"Your daughter has been what?!  Taken... by whom?"
"Please calm down, I can't help you unless you speak slowly.  I don't quite understand you..."
"You say your daughter violated the one-child policy...  And local officials had her sterilised.  She had some sort of forced procedure in the hospital?"
"Wait, okay... I see.  This was many years ago.  She wants to present evidence to the central government.  Okay... and then she disappeared."
Before the conversation was over, I was already starting to gather my things together.
Liu Zhuying's daughter, Zhang Wenfang, had managed to call the night before and tell her mother where she had been taken - to a hotel in southwest Beijing.
I knew about these hotels. We had investigated them back in 2009.  Cheap places rented out by the block to officials to set up as ad-hoc prisons, known as "black jails".
They are illegal, of course, with no one imprisoned there given any due process. Most of the people in black jails are not petty criminals, but rather ordinary citizens who have stories of corruption to tell. Precisely because their evidence threatens the government, officials whose interests would be harmed by any revelations go after them.
We met Mrs Liu one block from the hotel. She had brought a group of friends with her.
As I followed her into the hotel, I noticed tape crossed in X's on the entrance - it was an abandoned building, no longer managed by its owners.  There was no electricity.  We walked up one floor, up another floor, then to the third floor in the dark.  She banged on the makeshift door that blocked off one wing of the building.
"Wenfang!  Wenfang!" shouted Mrs Liu, hoping her daughter would answer her call.
Black-clad men opened the door. They tugged Mrs Liu in.
Two years ago, I had knocked on the door of a black jail and had witnessed a woman screaming for help on the other side. I had been unable to stop the men when they shut the door in my face. I was not going to let this happen again - so I stepped over the threshold, and gripped the sill. A moment later, our team - together with the camera - stumbled into the hallway and the men scattered.
The rooms were empty. Mrs Liu's daughter had gone, although one of the men told us that she had been there and was safe.
In these moments, in my experience, two things can happen: the situation can become confrontational and threatening, or the black-clad men spot the camera and disappear.
By and large, people are not fond of being filmed acting like bullies, so the men scattered as we followed Mrs Liu, who by this time was sobbing, screaming, and throwing her arms up into the air.
Her friends - also other petitioners - had entered the building.
"They know black jails are illegal. They hold us here. I was in a black jail," said one man.
"You can't just grab people from the street anymore, you can no longer do this," said another, referring to the new criminal procedure law.
The criminal procedure law is due to be passed by China's legislature on Wednesday.  Under the new regulation, families must be notified within 24 hours following the detention of a suspect.
Black jails have never been legal, but if police had placed Mrs Liu's daughter somewhere in secret detention, they would now be bound to report it. It means that black jails and other forms of secret detention would not be allowed, except in extraordinary circumstances.
But standing in the hallway, it was very clear to our team that if there will be change, it would not take place overnight.
The petitioners surrounded me. They pressed in close, tugged at my sleeve, handed me photocopies of documents and testimonies they believed would help them in court - if they can ever have their day, that is.
I noticed that not only were many of the people old, but a number of them were on crutches, and I wondered what terrible stories were behind their disabilities.
One of them crumpled down to the dirty cement floor, exhausted from the brouhaha, and just looked up at me, the dirty and worn cardboard sign stating his grievance hung around his neck. These people live desperate existences, and in the back of my head, I knew that at some point, I'd get out of this building, and that I'd go home to central heating, a soft mattress, and a good meal.  I did not like the dissonance of all of it.
The inner Confucian upbringing in me also made me feel uncomfortable that anyone in their sixties or seventies would need to appeal to someone like myself - a young woman.  Shouldn't it be the other way around?
A sense of piety made me think that in another circumstance, I would go down the hall, boil some hot water, and bring them some tea, the way I would do for my grandmother.  Why are they begging me?  There was something fundamentally wrong, something topsy-turvy, about elders beseeching the child.
Their old, brown, wrinkled faces crowded in, and I was standing in the middle of this circle, the centre and the hope for them. They were orbiting around me, and the truth was, I knew I was not the harbinger of hope, and felt like a fraud, a misrepresentation.
A real challenge
When we interview people in China, we always make it clear to them that we can only report their story, that we can't change things or make things better for them. And I said this several times to the petitioners on this particular afternoon as a way of apology and embarrassment at my own feeling of helplessness. I could not do anything to change their situation.
We had come here to film visual evidence, to show that the enforcement of China's new criminal code would be a real challenge considering that basic violations of the law took place right in the capital.
Eventually, uniformed police officers arrived at the scene. They ignored the unidentified men who'd been managing the jail and showed no indication that they would shut down the jail.
Despite some efforts to come down on illegal detention facilities and some high-profile raids in recent years, police usually prefer not to get involved with those working in different departments and different jurisdictions. It is easier for them that way, even though I sensed the uniformed officer who dealt with us felt bad for the petitioners, and didn't think we had done anything wrong.
We were ordered to stop filming, and to leave.
Mrs Liu and her fellow petitioners followed us to our car. Different petitioners handed me documents, each one a story of abuse I would look over later back in our office: someone sent to a labour camp for half a year, a house burned to the ground by a local police officer, a farmer's land taken away from him.
To Mrs Liu as we stood by our vehicle, we wished her luck finding her daughter.  We repeated again that our report would likely not do her any good.
She didn't care.
She was just thankful that someone had listened to her story, and had cared enough to show up at all.