Lowboy by John Wray. 

William Heller, aka Lowboy, is on the run after breaking his conditions of release from Bellevue psychiatric hospital.  He travels the subways and subterranean tunnels, off his medication and becoming increasingly psychotic as his paranoid schizophrenia takes over tipping the human need to find patterns in the chaotic into madness.  Wray writes the novel from two points of view, Lowboy's increasingly disturbed perspective and that of Detective Ali Lateef, searching for Lowboy with his mother Yda, aka Violet, their tale too becoming unspooled as Lateef reflects on his altered identity, name changed when his father converted to Islam, and that of Yda.  Very good, but I prefer Tabitha Suzuma