Short answers, pulled from the story.
It was a four-month Japanese military operation from mid-May to early September 1942 in the Chinese provinces of Zhejiang and Jiangxi. The Imperial Japanese Army launched it in retaliation for the Doolittle Raid, with the goals of destroying Chinese airfields and punishing civilians who had sheltered American pilots.
After the 18th of April 1942 bombing of Tokyo, Nagoya, and Yokohama, most of the sixteen American B-25 bombers crashed in Zhejiang and Jiangxi after running out of fuel. Chinese civilians sheltered nearly all sixty-four surviving airmen. Japan used this as justification for massive reprisals against the local population.
Up to 250,000 Chinese died, the majority of them civilians. At least 10,000 were killed specifically for sheltering or assisting Doolittle's airmen. Japanese forces also lost over 1,700 soldiers to biological weapons they had deployed themselves, with the actual number likely higher according to a Japanese prisoner of war captured in 1944.
Japan's Unit 731 introduced nearly 300 pounds of paratyphoid and anthrax pathogens into the region. Contaminated food and wells were left behind near Yushan, Kinhwa, and Futsin during the Japanese withdrawal. Japanese troops then re-entered contaminated areas and suffered cholera, dysentery, and bubonic plague outbreaks among their own ranks.
General Shunroku Hata commanded the China Expeditionary Army. Commander Korechika Anami led the 11th Army, directing two divisions and four detachments in the operation. Chinese forces in the region were under Gu Zhutong, commander of the 3rd War Area.
Sixty-four American airmen parachuted into the Zhejiang area. Most were sheltered by Chinese civilians. Eight were captured by Japanese troops, and three of those were shot after a show trial on charges of crimes against humanity.