Well, without having read the 'I failed to throw the villain away novel', it's hard to say precisely. However, based on the title, it could involve a protagonist who has a plan to eliminate or distance themselves from a villainous character. But things go awry, and the villain remains in the picture, causing trouble for the protagonist, their friends, or the world they live in. This could lead to a story full of conflict, suspense, and the protagonist having to come up with new strategies to deal with the situation.
The character development of the villain could be so well - done. A complex and interesting villain can make the whole novel irresistible. They might have a tragic backstory that makes you want to keep reading to understand them better.
Since I haven't read the novel, I can't say for sure. But likely there is a protagonist who is the one trying to throw away the villain, and of course, the villain themselves.