Luck in the Shadows (The Nightrunner Series, Book I) by Lynn Flewelling is $2.99 in the US.
I read this book many years ago and while the memory of the details are somewhat hazy I know I went on to read the rest of the series
https://store.kobobooks.com/en-us/eb...in-the-shadows
https://www.amazon.com/Luck-Shadows-.../dp/B00486U8JK
When young Alec of Kerry is taken prisoner for a crime he didn’t commit, he is certain that his life is at an end. But one thing he never expected was his cellmate. Spy, rogue, thief, and noble, Seregil of Rhiminee is many things–none of them predictable. And when he offers to take on Alec as his apprentice, things may never be the same for either of them. Soon Alec is traveling roads he never knew existed, toward a war he never suspected was brewing. Before long he and Seregil are embroiled in a sinister plot that runs deeper than either can imagine, and that may cost them far more than their lives if they fail. But fortune is as unpredictable as Alec’s new mentor, and this time there just might be…Luck in the Shadows.