This is about gain-of-function research that the USA stopped in 2014 for safety reasons.

Gain-of-function is adding features to viruses. A goal of her research was to add functionality to coronaviruses that could infect humans. With funding stopped in the USA, she moved to Wuhan to continue her work.

The timeline runs for years, right up to December 2019. It includes a SARS coronavirus escape in 2017 that was caused when lab workers failed to properly inactivate the virus before taking it out of the BSL-4 high-containment facility.