Sunshaker's War - David Sullivan, #4

WAR OF THE WORLDS An evil brew has boiled over in the mystical realm of the Sidhie.a great conflict has devastated the lands of Faerie-and its earth-shaking repercussions can be felt across the boundaries of the mortal lands. Young David Sullivan has been to the Otherworld, and knows of its mysteries.and its terrors. Now he must somehow find his way past the magically sealed borders of Tir-Nan-Og-for the life of a mortal friend hangs in the balance.
And if the dreaded war continues unchecked, the harnessed power of the Sun will unleash the forces of chaos and death in two separate worlds on Midsummer's Day.  "Deitz  gives every indication of having several more equally impressive tales up his sleeve. Few writers match personal crisis with epic conflict as effectively." Dragon