My Sister the Serial Killer by Oyinkan Braithwaite
During her dinner one night, Korede receives a distress call from her sister, Ayoola. She knows what's expected of her: bleach, rubber gloves, nerves of steel, and a strong stomach. Apparently, this is the third boyfriend Ayoola has dispatched in self-defense, and the third mess her lethal little sibling has left for Korede to clean up. Probably, she should report to the police for the safety of her fellow menfolk in Nigeria, but family comes first, as they say. Ayoola is dating Korede's doctor until she starts dating Ayoola's doctor. Korede has long loved him, but at the same time, seeing him die with a knife to the back isn't what he wants.
It's bitter for Korede. Is it possible for her not to be? Besides being her favorite sister, Ayoola is also beautiful and possibly sociopathic. Now, Ayoola's third boyfriend is dead. The sisters' saving grace is Korede's practicality. Ayoola keeps posting pictures of her dinner to Instagram when she ought to be mourning the loss of her "missing" boyfriend because she knows how to clean blood and her trunk can hold a body. She doesn't get any credit for that.
The hospital where Korede works is home to a kind and handsome doctor who becomes her partner every now and then. She dreams of the day when he will realize how ideal she is. When he requests Korede's sister's phone number, she must consider the extent to which Ayoola has deteriorated and how far she will go to protect her.
The debut novel of Oyinkan Braithwaite is sharp as nails and filled with deadpan wit, making it both entertaining and frightening.