Arriving in Merida, a small city on the northern coast of Yucatan, Hop, Tank and young Christopher Cross began an intensive aerial search for the ruins of a lost Mayan city where they hope to find an ancient mural that would help the United States conquer the barrier of supersonic flight. In a long wide sweep ranging over the tropical forest Chris saw nothing he recognized and the boys discouraged, return to Merida to spend the night. Tank stayed on to watch at the plane to prevent being surprised by their deadly enemy La Plantera but in the last episode when Hop and Chris returned from dinner to relieve Tank, they found both the plane and the mechanic gone and in the hanger La Plantera's Cessna.

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