When an exiled prince unexpectedly becomes ruler in a foreign kingdom, he must make dangerous alliances if he is to survive the vampire Emperor who murdered his parents.

>>>?the hook is the vampire as a ruler

That could be a problem.? It takes a great villain to make a great hero, yes But the protagonist must possses some defining characteristic that makes him a character who accrues sufficient emotional investment on the part of the viewing audience.? Whose struggle will engage their interest such that they will root for him and stay tuned in week after week to see what happens next.

And a protagonist has to be proactive, at least as proactive as the antagonist.? And I'm not sure he is.? Taking the logline at face value, he doesn't intentionally win the throne in another kingdom.? Rather, it's given to him "unexpectedly" after he flees into exile.? He's one lucky guy but is it luck he's earned the hard way or luck that's been give to him by others?

And since this is a fantasy what particular magic does he have -- or has the need to develop and use wisely -- to counter the magical power of the vampire?

Finally, have you considered making the story with a female protagonist?

>>>?the hook is the vampire as a ruler

That could be a problem.? It takes a great villain to make a great hero, yes But the protagonist must possses some defining characteristic that makes him a character who accrues sufficient emotional investment on the part of the viewing audience.? Whose struggle will engage their interest such that they will root for him and stay tuned in week after week to see what happens next.

And a protagonist has to be proactive, at least as proactive as the antagonist.? And I'm not sure he is.? Taking the logline at face value, he doesn't intentionally win the throne in another kingdom.? Rather, it's given to him "unexpectedly" after he flees into exile.? He's one lucky guy but is it luck he's earned the hard way or luck that's been give to him by others?

And since this is a fantasy what particular magic does he have -- or has the need to develop and use wisely -- to counter the magical power of the vampire?

Finally, have you considered making the story with a female protagonist?

Yeah, but this context then should be in a summary-like text. The only thing I can think of to add to the logline without making it too long is change vampire for blood sucking emperor

"When an exiled prince unexpectedly becomes ruler in a foreign kingdom, he must marry a trecherous king's daughter if he is to reclaim his throne or die in the hands of the blood sucking emperor who murdered his parents.?