Ollie and Moritz are two teenagers who will never meet. Each of them lives with a life-affecting illness. Contact with electricity sends Ollie into debilitating seizures, while Moritz has a heart defect and is kept alive by an electronic pacemaker. If they did meet, Ollie would seize, but turning off the pacemaker would kill Moritz. Through an exchange of letters, the two boys develop a strong bond of friendship which becomes a lifeline during dark times – until Moritz reveals that he holds the key to their shared, sinister past, and has been keeping it from Ollie all along.