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, references to the Middle East and TV celebrity chefs, 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 OR Nigel's ghost-hunting results in the first place.The documents Nigel stole depict a supernatural Swirly Energy Thingy very similar to the one in Ganwulf's tomb. Letting Nigel get interested in the Lost Crown, and recruiting to investigate the ghosts that could lead him to it, 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 ( Mr. Gruel) 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 the old Net Hut. One of the cats was left in the chest too long, and suffocated, creating a meowing ghost, exactly like the one that he later hears behind the door to the Nightmare Room. After Nigel occupied Harbour Cottage, she couldn't use it anymore, which is why Mr. Tibbs was strong enough to escape her at the Hut. Then she framed Gruel to deflect the investigation when Nigel and Lucy uncovered evidence of her crimes.
The "Hardacre" Nigel meets on his first night in town was one of the Agers impersonating the professor.The figure Nigel follows keeps fading away, too quickly for the fog to account for it. Hardacre later denies having met Nigel, and repeats many of the same statements he'd appeared to say on the Harbour Wall, evidently unaware that Nigel's heard those same remarks before. If the Agers have been watching Hardacre every spring to make sure he isn't getting close to the Crown, they'd know which turns-of-phrase he prefers to use when he chews out rival treasure-hunters to run them off and/or creep them out. We also know they can shift from their appearance in life to columns of black smoke, and they're clearly more powerful than most of the other ghosts in the story, so adopting another person's appearance may not be beyond their abilities. Normally, they wouldn't bother to start plaguing a would-be Crown-hunter until the trespasser got dangerously close to its hiding place, which is presumably why they hadn't killed Hardacre years ago. However, the Hadden photos of the Chasm had enough of a supernatural aura of their own to worry the Agers: they know the other ghosts in the region have information about the Crown's location, and the photos' presence implied that this treasure-hunter might try to communicate with those ghosts, so the Agers tried to head off Nigel's investigation by scaring him off in Hardacre's guise.
Station Master used to work at Dowerton Station.There's a note left behind by the Dowerton station master in Dark Fall: The Journal, which says the station is being shut down and its staff will need to find work elsewhere. Embittered at having to fire everybody, the Dowerton station master returned to his birthplace in Saxton, and took up a post at its (much smaller) train station. He's relatively unaffected by the spookiness of Saxton because he'd already gotten used to such things in Dowerton: if anything, a town haunted by the Agers is less frightening than one stalked by the Dark Fall.