How do you thank writer/director Joss Whedon for donating to your Kickstarter campaign? With a gospel cover of the theme song to his cult TV show, apparently.

At least that's what former Law & Order star and current Flash star Jesse L. Martin (who, more importantly, is also a Broadway musical veteran) did after Whedon donated "an outstanding amount" to the Kickstarter for his new musical short film, The Letter Carrier.

The Letter Carrier tells the story of a black family hiding from slavery in secluded mountains in 1860, and Martin is working on the project with his Flash co-stars Rick Cosnett and Carlos Valdes. The trio came together to lend some gorgeous harmonies to "The Ballad Of Serenity," which Whedon wrote for Firefly. The director tweeted a link to the cover, exclaiming "OMG."