One night Dr Trescott’s house burns down. Henry Johnson, a black servant, heroically rescues the doctor’s son from the fire, but in the process is badly burned. Dr Truscott nurses him back to life but unfortunately Henry’s face “has simply been burned away.”

….

The doctor takes Henry into his rebuilt home. From then on his practice declines. From having been the most sought after doctor in the town, he becomes the least. A delegation of prominent citizens asks him to put Henry into an institution, but the doctor refuses. The story ends with his wife crying over the teacups: none of the ladies of the town will attend her at-homes any more, and she has laid out the tea things in vain.

Crane is generally considered one of the first modern US literary realists, but of course he is also a symbolist, as all realists are. The symbolism lies in the choice of the aspect of reality that is portrayed. You don’t have to know much to know what is symbolised in The Monster.