Archer, Chris

After weeks of searching the New York City catacombs for a centuries-old diamond buried by a pirate, George van Gelder and friends are stopped in their tracks when their underground enemy, Leroy, kidnaps George's father's new girlfriend and holds her for ransom in order to gain the treasure.

Elena Vargas, having just turned thirteen, begins having weird visions that she chalks up to some type of psychic experience, but she gets really frightened when she sees herself being chased by a creature with horrible black eyes.

An old pirate map leads George and his friends to a mysterious network of trap-laden tunnels beneath New York City.

George van Gelder and his friends, having found Captain Kidd's secret journal, now know for sure there is a priceless gem buried deep beneath New York City, but they soon discover the treasure is not going to give itself up easily.

Some teenagers hijack a UFO and escape into a future controlled by aliens.

Todd Aldridge, missing for nine months, returns to his home with no memory of the time he was gone, but it does not take long for him to discover that he is not at all the same person he was before.

Six children discover that UFOs are time machines which carry evil super-soldiers whose goal is to conquer the earth.

When Jack receives a note saying his life is in danger, he figures it is just a prank, but when Jack becomes fluent in languages he's never heard before, and he overhears someone talking about killing him, and he realizes his new intelligence will come at a high price.

On her thirteenth birthday, Toni Douglas discovers that she has special powers.