The Subterranean Secret

"" is the fifteenth episode from the first season of The Mysterious Cities of Gold.

Gomez's army attacks the Fort of the Black Eagle and Mendoza uses the stolen cannon against them, but knowing that Mendoza has a limited supply of ammo, Gomez pushes his assault. Tao fashions a set of makeshift hand grenades out of clay pots with the left over gunpowder and buys some time to plan an escape. Eventually the Incas are forced to abandon the fort and the children sneak out through a secret cave. Gaspard's soldiers spot them and give chase, but the children give them the slip by swimming through an underwater cave.

Mendoza tries to warn the people of the Fort about Gomez' coming attack. They ignore him until Esteban persuades them that Mendoza can be trusted. Using the stolen cannon, he fires two warning shots at the approaching Europeans but misses his mark by a very wide margin. The third shot combs Gaspard's hair, while the fourth and final shot lands inches in front of him. While battle ensues, Tao grabs the rest of the gunpowder. The children make bombs from earthenware jars, which hold off the attackers for a short while. When the Fort is breached, the defenders retreat to the High Peak. The children are cornered and escape into a cave, pursued by Gaspard and some soldiers. Tao tries out the echo, accidentally waking some vampire bats which slow down Gaspard and his men. The cave ends at a pool of water, but Tao finds an underwater passage through which they swim to safety, leaving Gaspard puzzled. The children are caught in a strong current, and finally find themselves at the foot of the waterfall near the High Peak.

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