What is the theme of the story "The Stolen Bacillus" by H.G. Wells?

One distinct theme of this story is that things are not always as they appear.  At the beginning of the story we are introduced to our two main characters:  a bacteriologist working in a lab in London, and his visitor, a man who has displayed some vague interest in the lab’s proceedings and been invited to come see the lab for himself.  This man is intensely fascinated by the dead strains of cholera shown him by the bacteriologist, and his eyes gleam with a strange fervor when the scientist produces a tube of live bacteria.

The bacteriologist finds his visitor harmless, despite his ” lank black hair and deep grey eyes, the haggard expression and nervous manner, the fitful yet keen interest” in the subject at hand.  And the scientist, who “had been told rhetoric was his weakness,” after describing in great detail the absolute destruction of the city should even the smallest drop of live cholera bacteria infect the water supply, notices his guest completely transfixed by the concept.  Soon after, we discover that this apparently harmless man is in fact an anarchist, intent on ravaging the city and bringing its people to ruins – with a strain of stolen bacteria.

And yet that bacteria itself is not what it appears – even though the bacteriologist begins a harrowing chase for the anarchist through the streets of London to retrieve his stolen test tube, and facing defeat the pale villain drinks the contents of the tube himself, to personally infect the people of London, it is revealed at the end that all his efforts were in vain.  The bacteriologist, whether to impress the man or just as a joke, we don’t know, misled him into believing the bacteria was actually cholera; it turns out it was actually a newly-discovered bacteria that, by all intents and purposes appears to turn its host blue.

So here we have a man who was not what he seemed – a harmless guest who turns out to be a psychopathic anarchist; and a bacteria that is not what it seemed – a deadly disease that is in fact merely the cause of a very embarrassing discoloration.  And, to delve deeper into the moral of the story, we can say that it seldom works to our advantage to deceive others, however nefarious or harmless the motive may be.