While in London, Peaches, Simon's faithful hellhound manages to grow to the size of a small bus, shocking Monty & Simon with his new transformation. Realizing the danger of a Peaches XL, the Montague & Strong Detective Agency take steps to control these growth spurts. They acquire a special collar to regulate the size shifts, but it's not working. The situation is growing out of control...literally.

Equipped with teleportation, eye-beams, impervious skin, and an insatiable appetite for sausage the time has come to train Peaches. There's only one problem—no one wants to train a hellhound. Running out of options, Simon finally discovers someone willing to take on the task...Ezra the personification of Death and trainer of Cerberus, Peaches' father.

Now with Death as his trainer, Peaches and Simon must undergo extensive hellhound obedience training. If they fail, they'll discover that there is a fate worse than Death. Will Peaches learn to control his abilities? Will he outgrow the situation and destroy the training facility? Will he ever get enough sausage?

Join Simon as he learns that a dog may be man's best friend, but a hellhound's love can dwarf any obstacle.