Obsidian Puma (The Aztec Chronicles #1)
Zoe Saadia

However, the great island capital with its towering pyramids and gushing industrial life was busy with its internal politics, disdainful of foreigners, especially barefoot villagers among those, indifferent to their small aspirations. A civil war was brewing, preying on everyone’s minds, and when the actual trouble erupted Miztli found himself in the heart of it, swept by the powerful surge that cared nothing for his private frustrations with the big city, thrown in with the most unexpected company: from pretty Chantli, the workshop owner’s daughter, to a pair of adventure-seeking noble school pupils Necalli and Axolin, to the wildest kid of them all, Ahuitzotl, the youngest brother of none other than the Emperor himself.
A fun escapade of sneaking into the underground tunnel full of hidden weaponry and other anticipated treasures turned out to be not as harmless as they expected, pitting them against ruthless smugglers and worse, unleashing a series of events none of them could have foreseen or foretold.