Upon arriving in New York from Ireland, "Mary" and "Tom" discover their uncle "Niall" is nowhere to be found. Their only connection seems to be a small dog that “Mary” grows fond of and names "Sparky." Believing he won't appear, they impulsively decide to head west to California in search of him. The difficulty arises when they realize train travel requires money—something they don’t have, and must quickly obtain within an hour. Alternatively, perhaps they could join a group of traveling children and sneak onto the train. These kids are orphans being resettled with foster families along the way; however, "Nick," who is paralyzed and uses a wheelchair, doesn't seem likely to be adopted. As they navigate friendships and evade the ticket inspector, they slowly make headway until trouble begins. This leads them into the hands of the dangerous Cheyenne, then to even more merciless bandits resembling “Lee Van Cleef,” who operate a gold mine using slave labor. The story follows their efforts to free themselves, rescue the miners, "Sparky," "Nick," and ultimately locate uncle "Niall"—which is where the entertainment lies in this fast-moving, visually distinctive animated film. It merges the bravery of early settlers with traditional Western adventures, incorporating elements reminiscent of “Temple of Doom” (1984). Reportedly inspired by true events involving siblings, it easily fills ninety minutes with moments of amusement as they traverse a huge and unexplored wilderness searching for someone lost in a very large haystack.

Source on TMDB