We all know the first line of a query is your "hook." I call the last line the "sinker." You want it to punch them in the face, in a nice, friendly kind of way that makes them unable to forget you after having read the 300 other queries in their inbox.
Also, for my brave Saturday Slash volunteers I will gladly do follow-up slashes (each more kindly than the next) on your query if you post them on the Query Critique board over on AgentQuery Connect. You'll get advice from me, and also people who are smarter than me. If you do post on AQ, be sure to follow the guidelines and let me know you posted so that I can follow up!
As the virus spreads so does their power. I definitely like the hook, but it does leave me wondering "who" b/c I'm kind of picturing tiny power-crazed amoebas. However, since that's literally cleared up three words later I think it's OK. Prince Anton’s family has long dominated their disease-ravaged planet. Blessed with genetic immunity, the treatments derived from their blood gives them control over a desperate public. But the rules Prince Anton made to protect the homeland of his estranged wife, Tia, now condemn her. Quite good. I think you can kill mention of Tia by name here though. It makes your last sentence clunky.
Guilt over a deadly accident they’ve kept secret for a decade took Tia and here we get her name and it's inferred that she's the estranged wife, so I think you can safely cut proper name insertion in first para and Anton down divergent paths; Tia becomes a leader in the liberation movement, and Anton head of the Unity Defense Forces. Now Anton’s obsession with saving Tia’s war-torn homeland from the disease has thrown both their lives into chaos. So -- Tia's homeland and Anton's are different? Just curious, b/c the idea that she's all Liberation makes me think of an internal revolt movement, and his government position sets them at odds. But if she's from a different place altogether I think it takes away from the mention of their political affiliations.
As eradication of the virus comes within reach, Anton’s vicious uncle, the Tsar Regent, cuts off delivery of all treatment kill the word "treatment" here doses to protect his political interests. Left with only the limited doses echo with "doses" - how about "supplies?" his own blood can provide, Anton continues to deport the infected, forced to dispose of rather than save them the last clause here makes for a long-winded sentence and is a tell after a show. When Tia uncovers the truth, and the local militias she’s funded fight back, Anton faces a choice clunky- rephrase . Fight his own nation for more doses, or continue with the protocols that now leave Tia ineligible for a dose. Hey mister - that's a question. You need a question mark. :)
Overall I think this is great. Highly interesting and unique premise. The major thing that's tweaking me here is the geographical confusion. Why would Tia care if Anton is deporting people from his country if it's not her country as well? Clear that up. I think you're looking good.