Oscar and his brother George were stolen six days ago from the Garnett family's back garden in Rainford.
Within 24 hours Oscar was dumped back at home with a broken leg and covered in cuts. George is still missing, leaving his brother and owners Peter and Trisha Garnett distraught.
Mr Garnett, of Dairy Farm Road, said: "George and Oscar have never been apart, and you would never see one without the other.
"Now Oscar won't leave our side and he is scared to go into the back garden. Our daughter Abbey is devastated.
"Oscar is making everyone sad because he looks so sad himself. We have had them since they were six weeks old and we would give anything to have them back together again."
Oscar is so upset by the loss of his constant companion that he has slept next to a mirror convinced that his reflection is his missing brother.