Episode Title:A Grim Retreat.Episode Description:The riders, tired and restless from overwork on defenses for the Edge, convince Hiccup to allow a much-needed vacation on a deserted island paradise. All is well until suddenly the dragons begin to wildly revolt, and the others assume Hiccup's obsessive work regime is to blame. Toothless appears to be the only exception until he too begins to rebel, but the riders discover to be the true cause to be freshwater-dwelling parasitic dragons called Grimoras. One by one the riders cure their dragons using salt water, and agree to take vacations at home while Hiccup promises to lighten up on his Viggo obsession. Meanwhile, Stoick and Gobber, left in charge while the riders are away, lose Tuffnut's pet chicken and each try to replace it with a new one.