Murder Is a Promise - Giammatteo Giacomo

No matter what kind of promise you make—it’s a promise. If you don’t plan on keeping it, don’t make it. 

In book five of the Friendship ' Honor series, Nicky goes to Brooklyn for a wedding. While he's there, Frankie has some trouble, and Nicky makes a promise to help him out.  

And remember, murder is a promise too.