The Cat with the White Mustache, book one, the case of the disappearing cat is the introduction of an angel cat who appears to a group of lazy cats who need to learn some lessons. The angel cat appears as a happy-go-lucky cat who wins some friends but alienates others in the group. The Cat with the White Mustache stays with the cats for a while but has a habit of leaving and then coming back within a few days or weeks.

It is the pattern of behavior that upsets some of the cats who do not like the Cat with the White Mustache. They believe he has another home where he gets good meals while they starve. These cats follow the "disappearing" cat and learn he left to protect a lady who was attacked by two big dogs.

The other cats who watched the Cat with the White Mustache saw him being attacked by one of the big dogs and they decided to help their "friend". These cats were able to force the big dog to leave but it was not until the Cat with the White Mustache had been killed. Saddened by their loss the cats returned to their home and grieved for the Cat with the White Mustache.

That evening the cats were gathered together when the Cat with the White Mustache appeared and he showed them he was an angel. He told them he came to their group to help them learn lessons of compassion and goodwill. When the angel cat left the other cats were overjoyed to know their friend lived and the moment changed their lives.