In a small pot, heat the water over high until boiling, then remove from heat. Add the hibiscus flowers and allow to steep for five minutes, then strain the liquid from the flowers and return the liquid to the pot. Add the sugar, then heat on low until the sugar dissolves completely. Remove from heat and allow to cool.
In a highball glass filled with ice, add the tequila, followed by the grand marier and lime juice. Top with ¼ cup of the hibiscus simple syrup, stir gently, and enjoy.