Subject(s): Time travel -- Juvenile fiction. | Vikings -- Juvenile fiction. | Best friends -- Fiction. | Imaginary wars and battles -- Fiction. | Adventure and adventurers -- Fiction. | Science fiction. | Fiction. -- Vikings. | Fiction. -- Time travel. | Paris (France) -- History -- Juvenile fiction. | France -- Paris. | Paris (France) -- History -- Juvenile fiction. | Science fiction. | Time travel. | Fiction. | History. | Juvenile works. | Adventure fiction. | Fantasy fiction.