Monster

What do you mean by "black cat" in the context of this story?

Oops my mistake. I meant, can we say that Armand is the monster in Desiree's Baby

Armand is certainly not a sympathetic character and sadly a reflection of many people during this era. I'm not sure if he is a "monster". I would think cowardly and a bigot but a "monster" in the modern context of the expression is debatable. Armand is a reflection of slave-era times which were definitely ugly for many reasons.