Collins has mastered Spillane's voice. His contributions fit so seamlessly with what Spillane has written, at least as far as this reader was concerned, it was impossible to tell the difference. They had collaborated often on projects before Spillane's death in 2006, so Collins does have some insight into the way the author worked. Clearly he profited from that insight. As to why Spillane set aside the story and never finished it himself, there doesn't seem to be any information, but as Collins says in a note at the beginning of the book, "it was a yarn worth finishing."
I would agree. Lady, Go Die! is a tale worth telling. There is a mysterious disappearance of a rich black widow operating a gambling casino who turns up naked draped over a statue of a horse, leading to a somewhat cringe worthy pun, and extremely dead. There are corrupt cops and city officials. There are fights and shoot outs. There are serial sex murders. Everything a thriller reader could want is there, if not always in the kind of detail he's come to expect.
At a time when graphic sex and violence have become almost a staple of the thriller genre, Spillane may seem almost tame, his talk of booze and broads almost archaic. True enough, there is a sense in reading Lady, Go Die! that you are reading a relic of what is now a fairly distant past. It makes sense that the story is set back in the 40s. Mike Hammer is a figure that belongs in that world. He is an important link in the chain between the Sam Spades and the Jack Reachers, and it would be a mistake to turn him into something other than the toughest of tough talkers, shoving a Lucky between his lips and lighting up as he tosses down a highball with a blond with plenty of curves in all the right places.