Lee was a co-owner of the Causeway Bay Books and the Might Current publishing house that specialized in selling books concerning the political gossip and other lurid subjects of the Chinese Communist party leaders. These books were banned from China, but were popular among the tourists visiting Hong Kong. Towards the end of October 2015, four co-owners and managers of the bookstore and publisher, Gui Minhai, Lui Bo (呂波), Cheung Jiping (張志平), and Lam Wing-kei, went missing from Thailand and mainland China, believed to be detained by the Central Case Examination Group. Lee had expressed concern of his safety in various interviews after his colleagues disappeared, and intentionally left all travel documents at home (confirmed by his wife after his disappearance).