The thriller The Inmate (affiliate link) by German author Sebastian Fitzek tells the story of a man named Till, who uses a false identity to infiltrate a mental hospital to find out what a famous child murderer did to his son.
The Patient is a quick read and the plot progresses quickly, there are no idle moments. There almost were too many characters for me to keep up with.
In the thriller category, this is in the better, non-boring category. I am interested in reading more books by this author.