Brother detectives Frank and Joe search a hidden castle for clues to help them find a missing comic book in the 19th book in the thrilling Hardy Boys Adventures series.

Frank and Joe are back on Black Bear Mountain, the scene of a previous wilderness adventure and mind-bending mystery. This time, the brothers are checking in on Dr. K, a friend they made during their first trip. Dr. K is a fan of living off the grid, but he’s been MIA long enough to cause worry in the small mountain town. And so the teenage detectives Black Bear Mountain relied on before have been called in to help once again.

Bayport High's Green Environment Conservation Club is camping on Black Bear Mountain. Not only does the mountain live up to its name - the fierce, furry animals are everywhere - but rumor has it that a madman lurks in the nearby forest, and the crazy dude has a penchant for feasting on human flesh. When the campers wake up, however, not only do they find a bear roaming the campsite, but their teacher is missing...and blood is streaked across his tent.

"Joe," I said, concerned, "hit the brake!" "I am," Joe said, pumping the pedal now. But the car didn't slow at all. The traffic light turned red as we hurtled toward the intersection. And suddenly I saw the one other car out this early on a Saturday morning - a huge Express Delivery truck! Joe screamed. I leaned forward, bracing myself against the dashboard. There was nothing we could do. It was speeding right at us!

"JOE!" Frank suddenly yelled behind me, but it was too late. A dark shape advanced on us from inside the doorway, and a bag was thrown over my head again. I could hear them doing the same to Frank too. Arms reached out and roughly pulled me inside....

First, a priceless painting disappears from the Bayport Historical Museum; then, two ancient samurai swords vanish from a private collection. A string of robberies has hit Bayport, and all signs point to the Phantom, a recently released ex-con who last struck more than 20 years ago. There's only one problem: The Phantom has vanished into thin air, and not even Frank and Joe Hardy can track him down.

The Hardy brothers and Frank’s new girlfriend, Jones, are attending a local comic book convention on the shore. They meet up with Jones’ friend Harper, a fellow comics super fan, outside the convention. The four of them spend hours running from booth to booth and end the perfect day with pizza at Harper’s short-term rental apartment. Things don’t stay so perfect, though. On the way home, Jones realizes she switched phones with Harper by accident and she's getting some really scary texts. They show up at the apartment the next day to find it totally destroyed and Harper missing.

As I rounded the corner, I spotted Rick just ahead. He paused and bent down to poke at something on the ground by his feet, muttering something that I couldn't make out due to the wind. WHOOSH! I gasped and jumped back as a huge pile of snow slid off the roof of the ski shack, completely burying Rick!

Everyone in Bayport can't wait for the biggest event of the season: the premiere of G-Force - the newest ride by the world-renowned Piperato Brothers. Their creation is going to change the fortunes of Funsport, Bayport's small and recently run-down amusement park. Frank and Joe are friends with Daisy Rodriguez, the owner's daughter, and are first in line for the ride's launch. Purple lights click off, a huge whoosh emanates from the floor, loud music pulses....

An original Sherlock Holmes manuscript was stolen from the Bayport Museum and now pages keep showing up in Frank and Joe's things: their lockers, menus, even the backseat of their car. It's clear someone is out to frame them. But who could it be? The boys try their usual means of deduction, but everything leads to a dead end. They just keep finding unsuspecting people who were paid to hide the pages by a mysterious third party. Frank recognizes this tactic - it's exactly what Moriarty would do to throw off Sherlock Holmes. So the brothers decide to use one of Sherlock's signature ideas.

The world's largest reef exhibit is coming to the Bayport Aquarium. Frank and Joe are stoked for the unveiling of Predator Reef, a 300,000-gallon tank that houses small sharks, rays, and thousands of colorful fish. It's also home to the aquarium's new mascot, Captain Hook - a rare and valuable, 500-pound, giant sea turtle.

A wave of motion rippled through the cattle as they broke into a run. The cows directly behind Sarah and me looked back anxiously. The entire herd would be upon us in no time. Sarah cupped a hand to her mouth. "Clear out of the way! Stampede!"

One of the Hardys’ favorite writers, Nathan Foxwood, has recently died in a tragic car accident. Now, the press is swarming his house in Bayport to get the scoop on the novel he completed just before his untimely death. When Joe hears that Nathan’s wife is having a giant estate sale, he drags Frank with him. Who could pass up the opportunity to see inside their favorite author’s home? Nathan’s wife says she wants to get away as quickly as possible. She’s sure the house is haunted. But Nathan’s assistant, Adam, is not so willing to blame it all on the supernatural.

It does not take much to convince Frank and Joe to be extras in the new zombie movie that's filming in Bayport. Not only do they get a behind-the-scenes glimpse of the magic that goes into making horror movies, but they also get to wear freakishly realistic zombie makeup that makes them look like the walking dead! But the horror gets a little too real when disaster hits the scene.

The Hardy Boys are visiting Paris! Joe is excited to check out all the street art he's heard about. And Frank can't wait to go to all the museums he's researched. On their very first day in the city, the brothers are woken up early in the morning by fireworks. But these are no ordinary fireworks. They are a part of elaborate cover for the heist of a priceless artifact.