The Radio Witch of Battersea

During wartime blackouts, occult detective Henry Marlowe is summoned when a string of murders leave victims with chalked sigils and radios babbling in dead tongues. Clues point to a riverside laboratory where reclusive Dr. Viktor Kline—once a government physicist—has mounted a daring escapade: an "etheric oscillator" of vacuum tubes and coils intended to broadcast commands through the air. As sirens wail and spies close in, Marlowe must outwit both mad science and a thing that answers when the valve glows, or London will hear a new kind of terror.