After Pongo and Perdita's 15 Dalmatian puppies have been stolen by Jasper and Horace, Scottie asks Danny who was barking. Danny replies that it's Pongo and tells Scottie that 15 puppies have been stolen. They both signal the other dogs to form a "Twilight Bark," and their message is reached to Towser, who then sends it to his friend, the Colonel. Scottie isn't seen for the rest of the film, but it can be assumed that the puppies have returned home, and it was Cruella who was behind the 'dognapping' theft.
He also appears as a cameo, along with other dogs, during the "Twilight Bark" sequence. He is the first to pick up the Dalmatian puppies' barks. Though, it is possible that this could be a different Terrier, since their Human refers to them as a Female?