Newt is Albus familiar, a cat who can assume a humanish form. Albus begins to notice odd behavior and realizes that there is a new witch/wizard in the area who brought their own familiar Graves, a cat as well or maybe a dog? Either way after a few tense meetings Newt and Graves get along well, a little too well actually.
Thus beginning the courting of Newt with dead animal gifts, wooing songs at 3 am and other animal behaviors Newt adores but is very taxing on Albus.
The end being Newt finally getting fucked silly but also extremely loud in bed, as cats tend to be.