The Secret of Skull Mountain (1948)
by Franklin W. Dixon
(#27 in The Hardy Boys)

The Tower Treasure

The House on the Cliff

The Secret of the Old Mill

The Missing Chums

Hunting for Hidden Gold

The Shore Road Mystery

The Secret of the Caves

The Mystery of Cabin Island

The Great Airport Mystery

What Happened at Midnight

While the Clock Ticked

Footprints Under the Window

The Mark on the Door

The Hidden Harbor Mystery

The Sinister Sign Post

A Figure in Hiding

The Secret Warning

The Twisted Claw

The Disappearing Floor

Mystery of the Flying Express

The Clue of the Broken Blade

The Flickering Torch Mystery

The Melted Coins

The Short-Wave Mystery

The Secret Panel

The Phantom Freighter

The Secret of Skull Mountain

The Sign of the Crooked Arrow

The Secret of the Lost Tunnel

The Wailing Siren Mystery

The Secret of Wildcat Swamp

The Crisscross Shadow

The Yellow Feather Mystery

The Hooded Hawk Mystery

The Clue in the Embers

The Secret of Pirates&#039; Hill

The Ghost at Skeleton Rock

Mystery at Devil&#039;s Paw

The Mystery of the Chinese Junk

Mystery of the Desert Giant

The Clue of the Screeching Owl

The Viking Symbol Mystery

The Mystery of the Aztec Warrior

The Haunted Fort

The Mystery of the Spiral Bridge

The Secret Agent on Flight 101

Mystery of the Whale Tattoo

The Arctic Patrol Mystery

The Bombay Boomerang

Danger on Vampire Trail

The Masked Monkey

The Shattered Helmet

The Clue of the Hissing Serpent

The Mysterious Caravan

The Witchmaster&#039;s Key

The Jungle Pyramid

The Firebird Rocket

The Sting of the Scorpion

Night of the Werewolf

Mystery of the Samurai Sword

The Pentagon Spy

The Apeman&#039;s Secret

The Mummy Case

Mystery of Smugglers Cove

The Stone Idol

The Vanishing Thieves

The Outlaw&#039;s Silver

The Submarine Caper

The Four-Headed Dragon

The Infinity Clue

Track of the Zombie

The Voodoo Plot

The Billion Dollar Ransom

Tic-Tac-Terror

Trapped at Sea

Game Plan for Disaster

The Crimson Flame

Cave-In

Sky Sabotage

The Roaring River Mystery

The Demon&#039;s Den

The Blackwing Puzzle

The Swamp Monster

Revenge of the Desert Phantom

The Skyfire Puzzle

The Mystery of the Silver Star

Program for Destruction

Tricky Business

Sky Blue Frame

Danger on the Diamond

Shield of Fear

The Shadow Killers

The Serpent&#039;s Tooth Mystery

Breakdown in Axeblade

Danger on the Air

Wipeout

Cast of Criminals

Spark of Suspicion

Dungeon of Doom

The Secret of the Island Treasure

The Money Hunt

Terminal Shock

The Million Dollar Nightmare

Tricks of the Trade

Smoke Screen Mystery

Attack of the Video Villains

Panic on Gull Island

Fear on Wheels

The Prime-Time Crime

The Secret of Sigma Seven

Three-Ring Terror

Demolition Mission

Radical Moves

The Case of the Counterfeit Criminals

Sabotage at Sports City

Rock &#039;N&#039; Roll Renegades

The Baseball Card Conspiracy

Danger in the Fourth Dimension

Trouble at Coyote Canyon

The Case of the Cosmic Kidnapping

The Mystery in the Old Mine

Carnival of Crime

Robot&#039;s Revenge

Mystery with a Dangerous Beat

Mystery on Makatunk Island

Racing to Disaster

Reel Thrills

Day of the Dinosaur

The Treasure at Dolphin Bay

Sidetracked To Danger

Crusade of the Flaming Sword

Maximum Challenge

Crime in the Kennel

Cross-Country Crime

The Hypersonic Secret

The Cold Cash Caper

High Speed Showdown

The Alaskan Adventure

The Search for the Snow Leopard

Slam Dunk Sabotage

The Desert Thieves

Lost in Gator Swamp

The Giant Rat of Sumatra

The Secret of Skeleton Reef

Terror at High Tide

The Mark of the Blue Tattoo

Trial and Terror

The Ice Cold Case

The Chase for the Mystery Twister

The Crisscross Crime

The Rocky Road to Revenge

Danger in the Extreme

Eye on Crime

The Caribbean Cruise Caper

The Hunt for the Four Brothers

A Will to Survive

The Lure of the Italian Treasure

The London Deception

Daredevils

A Game Called Chaos

Training for Trouble

The End of the Trail

The Spy That Never Lies

Skin &amp; Bones

Crime in the Cards

Past and Present Danger

Trouble Times Two

The Castle Conundrum

Ghost of a Chance

Kickoff to Danger

The Test Case

Trouble in Warp Space

Speed Times Five

Hide-and-Sneak

Trick-or-Trouble

In Plane Sight

The Case of the Psychic&#039;s Vision

The Mystery of the Black Rhino

Passport to Danger

Typhoon Island

Double Jeopardy

The Secret of the Soldier&#039;s Gold

Warehouse Rumble

The Dangerous Transmission

Wreck and Roll

Hidden Mountain

No Way Out

Farming Fear

One False Step

Motocross Madness