Mercy Men were medical mercenaries who've sold themselves to science at the Hoffman Medical Center. Jeff Meyer, obsessed with finding Paul Conroe - the man who killed Jeff's father - tracks him down, but Conroe seeks refuge in the Hoffman Medical Center. To continue his pursuit, Jeff must become a Mercy Man himself.

This was expanded from A Man Obsessed - which appeared as half of an Ace Double in 1955. Nourse wrote several other stories involving or centered upon the "Hoffman Medical Center" - but they are not closely related (don't expect common characters.) Most of Nourse's novels were juveniles and rather good; this is one of his few SF books aimed for an older market - and I recommend it.