Diary of a Neapolitan Mastiff IV: A Mastiff Hope

"In this exclusive final chapter of Diary of a Neapolitan Mastiff, the Petbuster goes to steal Kate's half of the friendship heart! But she has a few tricks planned" - Blurb

Diary of a Neapolitan Mastiff IV: A Mastiff Hope, or Mastiff Book IV or simply Mastiff IV, is the fourth book in the series and the final in the Original Quadrilogy. It was intended as the final book in the series until the beginning of the Sequel Quadrilogy three years later; the blurb still refers to it as the finale. Kate and Magic's journey is close to a conclusion, and Danny is returned to Pocket Kingdom. It's time for Kate and Magic to defeat the Petbuster and return Ava!

Plot
On December 27th, Danny is still imprisoned, until the Petbuster decides to teleport him home. Back in Pocketville, Kate and Magic also return from the big city on Earth, aware that the Petbuster is intending on breaking into their home to steal the friendship heart. Kate, Magic, Danny, William, and the two cat royal guards Balloon and Meela visit Steel Wool, a tough sheep who can train them to stop the Petbuster. Kate and Magic are put through various lessons and tests, before facing the ultimate challenge of crossing a high current river. Kate throws Magic to the other side of the river with rope, which he ties around a tree, allowing Kate to cross. Steel Wool makes Danny cross the river due to his repeated failures in previous sessions. The death field had also been covered in sugar after a mill was caught in it. That night, the Petbuster breaks into Kate's house through her father's window, and uses a spray to knock him asleep. He goes downstairs, but Kate plays a police recording on the television to trick him. The Petbuster notices Kate and goes after her, tripping on the wire they had placed. He chases them again, and Kate releases several balls from a box, causing the Petbuster to lose his footing. The Petbuster chases them up the stairs, and he steps onto a superglued step, temporarily trapping his foot. Further up the stairs, he steps onto a bunch of pins. When the Petbuster finally reaches the door the Kate's room, he opens it, causing a bucket of soapy water to fall onto his head and into his eyes. Dazed, he mistakes paper cutouts of Kate and Magic under a desk for them, and approaches them, allowing the real Kate and Magic to trap him in a net. Kate calls the police and the Petbuster is jailed. With the Petbuster arrested, stray dog Wallis frees Ava fron his house.

In Pocket Kingdom, Eva gives up her half of the Friendship heart, planning on snatching the whole heart during the final ceremony which will return Ava. The heart repairs itself as one, and during the ceremony, Eva jumps toward the heart, but vanishes as the ceremony finishes. Ava appears, and Soul and Gourt are jailed. Ava made a new blue friendship heart for herself, allowing Kate and Magic to keep the original red one.