This leads to The Saint becoming a cause célèbre among the British people, to the point where the government offers him not only a full pardon for past crimes, but also a job as a sanctioned crime-buster.

(He would revisit this decision, however, in the later story "The Impossible Crime" (featured in the collection Alias the Saint) and again in the novel, She Was a Lady.)

Templar and Holm are about to leave when they encounter a giant of a man named Rayt Marius, an evil tycoon who wants the weapon for his own purposes.

Meanwhile, Scotland Yard Inspector Claud Eustace Teal also finds himself getting involved, even though the identity of The Saint remains a mystery to him.

But first he must try to convince the inventor of the electroncloud to abandon the weapon; when the scientist indicates that he not only refuses to give up his work, but might also be mad, Templar reluctantly decides the man must die to potentially save the lives of millions.

Later, while being held at gunpoint by Marius and the prince, Kent reveals that he killed the scientist, but not before being given the man's final notes on the electroncloud.

In exchange for Marius and the Prince allowing the Saint and his friends Patricia and Roger Conway to go free, Kent agrees to hand over the documents.

It is noteworthy that "The Last Hero" was published on the same year as Olaf Stapledon's vast science fiction opus Last and First Man – an otherwise utterly different kind of book, yet Stapledon also included the plot element of a scientist inventing a terrible weapon of mass destruction, which must be suppressed, even at the cost of its inventor's life.

After this book, the character of Holm fades somewhat into the background for a time, although she would return to the forefront in the novella collection The Holy Terror.

Conversely, in the present book Charteris drops many hints that Norman Kent is in effect "fey", meaning doomed to die—for example, his hopeless but gallant love for Patricia Holm.

With reference to this book, Caroline Whitehead and George McLeod wrote: (...) Norman Kent is an archetypal knight-errant.

Not only physical threats to life and limb, but also the sometimes unavoidable necessity to perform dishonorable acts which would have reflected badly on the reputation of King Arthur/Simon Templar are taken unflinchingly by Sir Gawain/Norman Kent.