In his 1956 book “In the Winter of Cities,” Tennessee Williams printed a small and exquisite poem titled “Little Horse,” a tribute to his lover Frank Merlo. This poem ends:

Mignon he is or mignonette

avec les yeux plus grands que lui.

My name for him is Little Horse.

I wish he had a name for me.

Williams and Merlo were together from roughly 1947 to 1963, a stretch during which the playwright composed some of the American theater’s enduring classics, including “Cat on a Hot Tin Roof,” “Suddenly Last Summer” and “The Rose Tattoo.”

Merlo was a working-class New Jersey boy from an Italian family and a charming young war hero. When they met, Tennessee Williams was already Tennessee Williams, flush from the success of “A Streetcar Named Desire,” voluble and lit as if by klieg lights.

Not long into their relationship, Williams wrote in a letter to a friend: “Have I ever told you that I like Italians? They are the last of the beautiful young comedians of the world.”

Williams and Merlo’s years together are the subject of Christopher Castellani’s blazing new novel, “Leading Men.” Writing fiction is to no small degree a confidence game, and “Leading Men” casts a spell right from the start.