Henrietta Trout, Golden Shifter Book 4: Death at Stonehenge

Henrietta Trout, Golden Shifter, is on her scariest mission yet! Destruction of all Gribblers (they're shape shifters of the criminal sort), is vital to save mankind from evil schemes to conquer the world. Her first plan - eliminate the Council, and they're somewhere in the Himalayan mountains...
Next, something really bad is happening. Gribbler scientists are making a Serum of Obedience, to dish out like bottled water everywhere that influential people work. Even worse, they're developing sound waves that can destroy all important buildings throughout the British Isles, creating chaos and fear.
Shape shifters everywhere are gathering for the conflict, and Gran can hardly keep up with such a lot of tea-making. But it's count-down time - let battle begin!