Harry Treadaway (pictured) and Brendan Gleeson have proven to be very well-matched adversaries in this Stephen King drama. Treadaway is a killer with several twisted streaks, and Gleeson is the retired detective still haunted by the killer’s previous murder spree. And slowly but surely, Mr. Mercedes has proven itself one of the best TV shows of the later summer, heading into fall – and its momentum seems destined to continue.