The Lost Crown: A Ghost-Hunting Adventure/WMG

The little boy with the camera isn't the same "young Oliver" who keeps winning the Saxton Snappers contest.
His name is never stated, so he could be Oliver's kid brother. The real Oliver might be home sick, or he could be sitting this year's contest out so his little bro can have a shot at winning.

Mr. Hadden is watching Nigel from the past.
The date of Nigel's recruitment and on the package Hadden sends for him are from 1978, yet Nigel is clearly from our own time (clothes, hairstyle, reference to the Middle East, etc). Hadden's note from the package suggests it was written after their phone conversation, even though he refers to the package having already been sent that morning during that discussion. Much of this can be reconciled if Mr. Hadden is actually observing Nigel by mystical means from 1978, and leaving directives to Hare and Crow that they can carry out in 2008.

Hadden never wanted the Crown in the first place.
The documents Nigel stole depict a supernatural Swirly Energy Thingy very similar to the one in. Letting Nigel get interested in the Lost Crown was just a sneaky way to gain access to one of those.

Morgan Mankle is the real catnapper.
Nigel hears a distressed cat's ghostly meowing from inside the chest in Harbour Cottage, yet the person arrested for the catnappings didn't have a key to that place. Morgan did have one, so could have used the Cottage to hide the kidnapped cats until they were weak enough to handle easily and she could sneak them into. One of the cats was left in the chest too long, and suffocated, creating a meowing ghost. After Nigel occupied Harbour Cottage, she couldn't use it anymore, which is why. Then she framed  to deflect the investigation when Nigel and Lucy uncovered evidence of her crimes.