The Hospitaller Oath by JD Kloosterman

Chad has escaped government prisons and half-angel fanatics to join with the Hospitallers, an ancient order dating back to the Crusades. But he's barely gotten started before he crashes (literally) into a plot involving strange mercenaries–Nephilim like himself–hunting down the Skofnung Sword, an ancient weapon of legend with amazing powers that could change the balance of power in Eastern Europe.

Thrown in with friends old and new, Chad soon finds himself falsely accused of kidnapping when he rescues Freyja Norjavik, a crippled arms heiress under threat of assassination. Chad's party must race across Europe pursued by the authorities, Russian commandos, and Freyja's two formidable sisters, as they seek to find the sword's elusive blade before it's too late. But there is a traitor in the party.

The second book in The Solomon Code series, this book follows on directly from the conclusion of The Nephilim Protocol. The Solomon Code series is an Young Adult/New Adult urban fantasy series centered on the legend of the half-angel Nephilim, which weaves together the folklore and history of countries around the globe to tell thrilling stories of adventure that touch on real-world issues.

“If you like Percy Jackson and other books that show supernatural adventures for teens this book is right up your alley fantastic writing interesting action-packed absolutely a great teen novel.” -Kranna, Goodreads reviewer