The Astra Signal. Book 2, #2

Pulled from their Dordogne refuge, Jean and Claire are thrust into a lethal shadow war: a Kremlin-backed syndicate, a corporate consortium, and a fanatical cult all want the Origin Signal for their own ends. The chase rips them from stone cottages and Alpine listening stations to Victorian crypts, storm-lashed Cornish cliffs, and the crushing black of the Mariana Trench. Their only advantage is a radical pact - the Vesper Clause - a two-person "key" that makes their partnership the final encryption.
As the mystery widens from moon-relays to planetary harmonics and a map of universal frequencies, Jean and Claire must decide what they will sacrifice to save the world - and whether two people can become the keystone in a cosmic design. Techno-Gothic, taut, and cinematic, The Astra Signal: The Vesper Protocol is a spy-sci-fi novella about love, trust, and the price of keeping the lights on.