For all those waiting for the next book in the Henderson Boys series, the wait is over.  Grey Wolves, the fourth in the series, has arrived in store. Grey Wolves carries on the story set during World War II:

“APRIL 1941:  With no European allies, Britain has to ship fuel, weapons and more than half of its food across the Atlantic from Canada and the United States. But slow moving cargo vessels make easy prey for packs of German submarines.

(From the Henderson Boys website which you can view here)

For those who are not familiar with the series, the series is generally recommended for age 12 and over and starts with The Escape.  In this book, Hitler’s army is advancing towards Paris, and millions of French civillians are on the run.  Amidst the chaos, two British children are being hunted by German agents.  British spy Charles Henderson tries to reach them first, but he can only do it with the help of a twelve year old French orphan.  The British secret service is about to discover that kids working undercover will help to win the war.  For official purposes, these children don’t exist.  (From the blurb of the book)