I have finished my first novel and shared it online with beta readers and those helping me write query letters. I checked Google to see if my very narrow niche market of "biological warfare" spy novel remained uncrowded. Most spy novels usually center around nukes or terrorists, but my specialty niche is about 'Germ Spies'. I was shocked to find there is now one published novel that is basically a version of my own. The published novel used my main protagonist's same name in its title (it is a rare surname with a unique spelling). The plot was indeed about espionage with biological weapons involving Russia, nearly exactly as my own novel. The author posted his novel on Goodreads where it received a single review from a newly created account, and this single review was the only time that account showed any activity. The reviewer also used the exact name of another of my main characters, a name that is very rare.
I have no real way of proving plagiarism of my plot and characters, especially since the other novel is self published, but in science we must disclose 'prior art' pertinent to our invention. My question is, since another author is using my main character's name in his novel with a plot very similar to my own, am I now required to change my characters name to avoid being accused of plagiarizing his work?