A Hong Kong publisher specializing in books banned in China has disappeared mysteriously, sowing fear among Hong Kongers that the Chinese government is growing bolder about encroaching on their liberties. As the saga continues to unfold, Beijing is reacting bizarrely, and in ways that suggest that the story is the extension of a long-running power struggle at the highest levels of the Chinese Communist Party.

Mighty Current is an obscure Hong Kong publishing company that churns out gossipy titles about China and its top leaders. On Dec. 30, Lee Bo, 65, an editor at the company, received a phone order for a dozen books, including several about the private life of President Xi Jinping. That evening he went to get the books in a warehouse in a quiet part of town. He never returned. Two of the company’s co-owners and two employees had disappeared before him, one after the other, beginning last October.

Within days of his disappearance, Mr. Lee called his wife, and faxed a message to colleagues saying he was “O.K.” and had gone to China “in his own way.” This was ominous, for his wife had found Mr. Lee’s travel documents at home; she began to worry that he had been abducted and forcibly brought to the mainland by Chinese government operatives.

Concern deepened after the mainstream Hong Kong newspaper Ming Pao reported that the local police were in possession of footage from surveillance cameras at the book warehouse showing Mr. Lee being shadowed by strangers as he walks into an elevator. A witness claims to have seen him being forced into a car by several men and driven off.