The Invaders Plan

Volume 1 of 10 books (Dekalogy) in the Mission Earth series.
Earth is to be invaded and a royal engineer must cross 22 light years to secretly infiltrate the planet. He is also crossing a scheme to use the resources of Earth's most powerful figure to overthrow the confederacy.

With a convicted murderess who trains giant cat like animals, a doctor who creates human biological freaks, a madman who controls Voltar's secret police and a clandestine Earth base in Turkey, a bizarre stage is set and narrated by an alien killer assigned to sabotage the mission and Earth, a planet that doesn't exist.