According to NBC:
Kings is an inspiring exploration of the timeless David vs. Goliath struggle. The show is set in a modern metropolis under siege, where the fighting has gone on for too long and cost far too many lives. When David Shepherd, a brave young soldier, rescues the king's son from enemy territory, he sets events in motion that will finally bring peace. Suddenly, David is thrust into the limelight, earning the affections of women - including the king's daughter. When he's promoted to Captain, he becomes the reluctant poster boy for hope. But for David, the line between his allies and enemies will blur as the power players in the kingdom go to great lengths to see him fall.
And now in Queerty's words:
King Silas Benjamin (played by Ian McShane) showers all of his attention on handsome hero soldier David Shepherd (actor Chris Egan), who saved the life of his son, Prince Jack Benjamin (played by Sebastian Stan), in war. But Prince Jack is gay! Which means the king would rather leave his throne to his son's savior, who is macho and straight and, unlike Prince Jack, does not have a gay boyfriend!
Will Kings rise to power, or be knocked off its throne? Tune in Sunday, March 15!