#plunkush?

Plunkett/Rush

Consider the science/apothecary/chemistry aspect.

Consider colonial-era!Rush being a scientist travelling to America to study new and interesting things (animals, plants, astronomy, I dunno?) and meeting a mysterious man who seems to be running away from his past.

Consider Rush finding out what Plunkett’s wife died of and having to shut it face because he knows a treatment/cure that maybe could have saved her.

Or, alternatively, consider space-age!Plunkett, a charming roguish scientist with a darker past than even Rush, getting trapped on the Destiny with the rest of the crew.