When Cody, Carly, and Jake find a treasure map in Cowlamity Kate's attic while cleaning it, they decide to follow it to find Tom Duggery's lost silver on Skull Mountain. While competing against Saddle Sore and Boot Hill Buzzard, Cody, Carly, and Jake encounter Tom Duggery's ghost in the form of Skull Duggery. Now Moo, Dakota, Cowlorado, and Cowlamity Kate must rescue the kids from Skull Duggery.