Stephen Hayes 
On the String [EPUB ebook] 

The sixth instalment in the Magic Crystals series, following the climactic events of 'The Cloak of Steel'.
Fresh off their victory over the evil Arnold Hammerson, John and his friends are left to rest and recuperate from their labours while the Sorcerers set about healing the world of its many war wounds.
However their victory is short-lived, as a new threat quickly arises and strikes back, stealing all their magic, destroying their sanctuaries, and magically warping the minds of many to fall in line.
Through nothing but luck, John and five of his friends are the only survivors, and must now resist their foe with no allies, no shelter, and no magic of any kind.
Their only good fortune is that the new enemy does not wish for their deaths, but intends to manipulate them into joining them of their own free will.
As the small band of rebels is left to dangle on the string of fate, the odds stack up wildly against them, and discord is sown among them in an attempt to loosen their resolve.
Yet in spite of all of this, they are able to cause serious problems for the adversary, and ultimately to find that the key to victory may lie in the not too distant past.