A Raucous Time (Celtic Cousins' Adventures #1) by Julia Hughes

Rhyllann and his cousin Wren are in trouble.  There were men trying to find an old book that Wren had acquired while working with an old man who loves books.  Grandma ends up in the hospital and Wren's foot gets hurt.  Crombie knows the two boys are lying.  He also gets the idea that Wren is the mastermind behind the odd happenings.  But he has more problems than that...

The author and Instafreebies sent me a copy of this book to read for review (thank you).  It has been published and you can buy a copy now.  

Legend says that a fortune was lost during bad weather a long long time ago.  Wren thinks the book he found will help him find it.  Rhyllan is conflicted.  Having money would be nice but he's not sure if he believes it will really be there.  Plus he has the cop breathing down his neck.

There's lots of action, corrupt cops, and mystical magic that only works because the boys are Celtic.  Those who touch the sword otherwise pay with their life.  At the end of the story, the boys split up.  But Wren is back on his doorstep before the last page.  This adventure isn't over yet.