With the engagement of Jonathan and Myste finally settled, they are ready to begin their new life together, traveling to Londinium upon the newest and safest airship of the day, the Zephyr. But neither Xavier Redstone nor Henrietta Eaton-Young have forgotton Jon. Bombs have been planted somewhere in the airship, and unless Saul Sherlock and Jack Watson can decipher the clues, this flight of the Zephyr will be its last.