A Vietnamese refugee of Chinese descent, Sandy Phan-Gillis spent the past three decades forging stronger partnerships between her family's motherland and her adopted home of Houston, leading dozens of delegations to China and even accompanying Police Chief Charles McClelland on a recent trip.

At home, she endlessly hosted Chinese groups, founded the city's Chinese New Year festival, and headed the Houston Shenzhen Sister City Association. Improving relations with China was her "life's work," her husband, Jeff Gillis, said.

But last March, Chinese authorities detained Phan-Gillis as she accompanied Houston city officials on a routine business trip, taking her into custody as she tried to cross onto the southern China peninsula of Macau. In two obscure text messages she sent to her travel partners, she told them to go on without her as she was attending to "personal business."

By the time her husband in Houston suspected something was wrong and called the U.S. Consulate in Guangzhou, Chinese officials had already notified them that Phan-Gillis was in custody for allegedly being a spy and stealing state secrets.

"It takes a second to wrap your head around this," Gillis said Monday. "Your spouse has been detained by Chinese spies. I mean, it's crazy."

Gillis is now publicizing his wife's ordeal to coincide with the U.S. visit this week of China's President Xi Jinping in hopes of placing pressure on U.S. and Chinese authorities to secure her release. Gillis said he has been working with the U.S. State Department and the U.S. Consulate in China since she was taken into custody but has yet to receive any answers as to why she is being investigated.

Neither the Chinese Embassy in Washington D.C. nor China's Foreign Ministry in Beijing returned calls or emails Monday. The U.S. State Department said it would respond Tuesday.

Can be detained six months

Gillis said the situation appears to be worsening and he is unveiling a social media campaign and website known as Save Sandy to focus attention on her plight. He said Chinese authorities moved Phan-Gillis into a more secure detention center, called Nanning No. 2., over the weekend, indicating the allegations against her may be more serious, though she has yet to be charged with a crime.

Under Chinese law, authorities can detain suspects for six months while they investigate allegations, said Simon Tang, a Houston lawyer representing the Gillis family who is in close contact with the Chinese lawyers they have retained there. After that period, the government has a month to issue charges or present its case in court, though it can obtain up to three extensions, totaling a delay of about another six months.

"We know very little," Tang said. "She's suspected of stealing national secrets, but we have no knowledge of what evidence they have ... It's getting more serious."

The 55-year-old naturalized American citizen and mother to a 29-year-old daughter in Seattle was accompanying a trade delegation including Houston's mayor pro-tem, Ed Gonzalez; his chief-of-staff, Houston businessman Vincent Chau; and Gary Ge, a Chinese businessman. Gonzalez said it was a routine trip promoting trade in Houston.

"There was nothing out of the ordinary," he said. "It was pretty much uneventful, just a series of meetings."

The group had been in China for about a week, stopping in Qingdao, Beijing and Shenzhen, and were passing through immigration to go from Guangzhou to Macau, a peninsula near Hong Kong. The group was separated as they went through the border crossing and were waiting on the other side for Phan-Gillis to come through.

"Sandy was nowhere to be found," Gonzalez said. "But it was daytime, it was busy, and there was nothing out of the ordinary, so we thought maybe she had gone to the restroom."

'We were concerned'

Chau stayed behind to wait for her but after she didn't appear he returned to the hotel. Gonzalez said Phan-Gillis later called Chau to say she was "taking care of a personal matter."

"I thought, man, that's bizarre. She should have let us know," Gonzalez said.

The group was supposed to fly back together from Hong Kong on March 21. But Phan-Gillis sent another text to Chau saying she was still handling a personal issue and would see them back in Houston, Gonzalez said.

"We were concerned but said we understand and let us know if there's anything you need," he said.

Phan-Gillis also called her husband and said she was going to stay in China longer than expected. He wasn't surprised. She often extended her business trips at the last minute. As the owner of PCI-Pacific Communications, she did consulting for U.S. and Chinese businesses and had several other companies registered in Hong Kong. It also wasn't uncommon for the couple to go days without talking when Phan-Gillis was traveling.

"It's not unusual for Sandy to call me at the last second before planning a trip home, especially if she's leading a group ... She'll put people on the plane and try to work on some of her own business while in China," Gillis said. "I was already expecting her to do that. It did not in any way strike me as unusual."

But by March 31, after Gillis hadn't heard from her again, he began to worry. When she did not reply to a frantic email, he called the U.S. Consulate in Guangzhou. They told him they were notified on March 23 that Phan-Gillis had been detained by state security services on March 20.

Gillis called the city of Houston's office of protocol and international affairs, which liaises with consulates, and contacted the Chinese consulate in Houston where he spoke to an official who had known Phan-Gillis for years. The official told him he considers her a friend.

"He said in his mind, Sandy isn't a spy or a thief," Gillis recalled. "But he also stated that he was not the decision maker, that he didn't have the power to help her."

Eve of Xi's visit

Gillis has two lawyers working on the case in China and is in close contact with the U.S. Consulate in Guangzhou, which meets with her monthly to check on her condition and relay messages from family and friends. They have reported that she is in stable health and receiving the medication she needs for high blood pressure and cholesterol, though she has been to the emergency room twice.

Gillis said his communication with the State Department has not been as positive as he would have liked and that he was told there are many U.S. citizens in prisons across the world.

He's hoping publicizing her case on the eve of Xi's visit will encourage U.S. and Chinese leaders to come up with a solution or at least provide him with some answers.

"I really want to get her out," he said. " I still don't understand what is going on. She has done so much for U.S.-China relations. It astounds me to think that China would act this way to a really good friend."