Black Knight tells the love story between a woman waiting for her true love and a man willing to do anything to protect her. Spanning over two hundred years, the tale follows Moon Soo Ho, a businessman with a pure heart who hides his true self from everyone except Jung Hae Ra, a travel agent who has never traveled abroad. Soo Ho and Hae Ra grew up like siblings in Hae Ra's home, but were later separated. As adults, they reunite, and their love feels like destiny. Will their love survive the challenges and obstacles fate has in store for them?