Things are heating up on Siren. In an exclusive sneak peek from the fourth episode, "On the Road," Ryn (Eline Powell) appears hopeful that she will reunite with her mermaid sister, Donna (Sibongile Mlambo). We also see patches of Ryn's flaky, dry skin, a direct result of her not being in the water for days. Her fascination with Maddie's moon necklace, though, is what really has our minds racing. What could it mean? Watch the clip above ahead of Thursday night's premiere, and then take another look at the show's drop-dead gorgeous cast!