In 1943, when the Germans plan to send all Danish Jews to prison camps, Peter and Elise, eleven-year-old twins, face danger trying to help their Jewish friend Henrik escape to Sweden.

Book 2 in The Young Underground series. Peter and Elise race to rescue a downed British pilot when a bomber crashes into the icy waters of the North Sea. Will they find him before the Nazis do?

The Nazis were after them, and there was nowhere to hide - Twelve-year-old Peter and Elise Andersen have secretly taken on a risky new assignment delivering illegal newspapers for the Danish Underground! Bringing news of freedom and deliverance to the people of Denmark seems like the perfect way to help fight the Nazis until soldiers nearly sabotage their mission. Is class troublemaker Keld Poulsen spying on Peter and Elise? Will he report them to the Nazis? Armed with secret code names, Peter and Elise must elude Keld in spite of his threats. When the Nazis plot to raid newspaper headquarters, the twins rush to help their friends in the Underground but will they find themselves cornered by German soldiers?

After World War II, Peter and Elise seek to discover who is trying to destroy Uncle Morten for his work with the Danish Underground.

Just after the surrender of Germany in World War II, three Danish children are trapped aboard a renegade German submarine attempting to escape to South America with Nazi treasure.

In 1945, while taking a train to Copenhagen to meet the King, Peter and Elise meet a man with a strange clocklike device and later have other strange adventures and encounters

In 1945 in Denmark, thirteen-year-old brother and sister Peter and Elise try to help their Jewish friend Henrik when his mother and a friend of hers are arrested by the Russians and accused of being spies

Book 8 in The Young Underground for middle-grade readers. Barely escaping a plane crash, Peter discovers a concealed handgun in the plane's cockpit. What is Matthias hiding? Who is involved in the nighttime rendezvous?