Now at university Rachel and Gareth are leading separate lives, but once again normality is disrupted by strange events for them. Gareth has an alarming clash with an unknown Knight at a jousting Tournament at Warwick Castle and Rachel foresees a plot to kill Galahad and the knights. They go back in time to warn Galahad and Merlin with no idea of the dreadful consequences that will unfold. The plot to kill the knights thwarted, they are ready to leave until they discover that Gareth's life is to be threatened by a force that can follow him into their own time. Meanwhile malevolence is gathering in the forms of Rathyen and Morgause who capture Rachel and take her to Rathyen's caverns. Her rescue puts lives at risk and is fraught with danger. The powers of darkness have been disturbed and are to be unleashed upon them. The Battle of the Underworld will commence. An army of the undead from Hades will seek to destroy everything in its path and it will be Rachel and Gareth's mission to fulfill their obligations as Keepers of the Power to attempt to defeat it! The Battle of the Underworld will require great magic and the combined efforts of all of their friends. However, the results are surprising and the twins are left with even more unanswered questions and the mystery continues.