Detailed but short horror novel

Write a short horror novel about a guy called Devlin who moved from Ireland and away from his family to an average suburban neighborhood in America. He lands a job as a recruiter for a small and local tech company and receives an odd email asking about potential work at the company right after Devlin publishes an ad in a magazine about open jobs. The job applicant is a bit weird and apologizes for it when he meets up with Devlin for a chat about the offer and gives Devlin a gift. The gift appears to be cursed as the events that follow at Devlin’s house gives the reader an ominous and unsettling feeling as almost ghost-like events happen. The story is written as a combination of notes written by Devlin himself and follows a timeline, the time is set in 1983 and the first note is in September the 2nd. These dates are stated before every note. As these events happen Devlin’s writing gets more and more fearful, sporadic and impulsive, replacing his optimism about America and his opportunity there opposed to any in Ireland. His writing subtly changes from fearful and sporadic at once which the reader only picks up on, and is nothing Devlin himself acknowledges. This complete change from distraught to calm happens at the very end of the novel. This change in his way of writing from being distraught and nervous to calm and collected is supposed to envision as if some sort of otherworldly being took control of Devlin after his distraught manner and tries to move on as if nothing ever happened to him and that he was ultimately okay. Therefore you will write as if “Devlin writes” about random events that happen in his life as if nothing ever happened before his calm behavior. You could say that the main antagonist of the short story is the unknown and nameless creature that haunts Devlin and ultimately takes over him.