It has been a popular saying as far back as ancient Rome: there is nothing new under the sun. Requiem for an Assassin, the sixth and final John Rain adventure from ex-CIA agent Barry Eisler, reminds us that there is also not much new under the rain.

All the signature elements of Eisler’s series, so well known to his legions of fans around the world, are found once more in Requiem. The exotic locations, attention to detail, and insiders’ knowledge of the world of espionage are rolled out again for this final chapter in the saga of Japanese-American killer-for-hire John Rain. But as another old saying goes, if it ain’t broke, don’t fix it. Eisler has had worldwide success with the formula that drives the Rain thrillers, so no need to change it now.

In the previous installment, The Last Assassin (2006), Rain was considering retirement and tentatively looking for a way out of "the life." Yet he was inevitably drawn back in, unable to escape the machinations of his past and too ambivalent about his possible retirement to carry it out; it was mostly in his head, not his heart. After all, Rain still seemed to get considerable enjoyment from the strategic, tactical, and physical aspects of the elimination of his targets — just like the reader.

This time out, Rain’s heart is drawn more and more to his son Koichiro, whom he may never know, and the only woman who seems to understand him, the ex-Mossad operative Delilah. These temptations represent escape from the realities of his difficult profession, and now he looks genuinely committed to pursuing them.

Yet once again, Rain is pulled back in, forced into service by a shady figure (is there ever any other kind?) from his past. Jim Hilger, a rogue ex-CIA operative based in Hong Kong, wants Rain’s services but cannot secure them through a conventional contract since Rain is nominally retired. Instead, he kidnaps Rain’s colleague, the marine sniper Dox, and forces Rain to kill three selected targets in exchange for his old friend’s life.

There are only a handful of people that the lone-wolf Rain would care about enough for this to work, but Dilger has picked the right one. Soon Rain finds himself in the familiar position of researching, tracking, and eliminating a series of mysterious figures on a whirlwind tour of Silicon Valley, Amsterdam, and Southeast Asia, as the reader breathlessly tries to keep up.

Committing these killings under duress only serves to highlight the moral fog that often surrounds Rain and his work; is there really any difference between these assassinations and the other ones he performs? Do his current victims, about whom he knows next to nothing, really deserve their fates any less than others he has killed in the past, whom he believed were the "bad guys?" Can he ever really know for sure who is good or bad? In an effort to insulate himself from some of the implications of these questions, Rain creates an alter-ego for the cold-blooded killer inside, calling him the "Iceman."

Plenty of questions line up for the reader as well, arising from the drama at the heart of the plot. Will Rain successfully complete the killings and free his friend in time? Does the third target even exist, or is it just a set-up to make sure that both Dox and Rain end up as dead as the two previous targets? It’s not hard to guess the answers, but how we get there is still plenty of fun.

And this time, it really looks like John Rain is ready to hang it up for good. Finding himself drawn to a quiet family life while wrestling with the ambiguous morality of his work, Rain indeed seems ready for retirement; he cannot stay in the life forever, no matter what the "Iceman" wants. One can only hope that it is not also the end of the line for Barry Eisler’s writing career, and that he will create some equally memorable protagonist in the future. After all, Eisler possesses a unique talent for showing us the fascinating world of those "who live in the shadows so others can enjoy the light," as one of his characters so memorably puts it.