The Infernal Game Series by Rebecca Levene

"You died 20 years ago - WELCOME BACK" At the start of the Cold War, the British secret services formed the Hermetic Division, an agency charged with using supernatural means to defend the nation. It has only one mission: to find the mysterious Ragnarok artefacts, said to have the power to end the world. Now, two of the divisions most senior agents are sent on the trail of a corrupt Russian oligarch. The journey will take them across Europe and into the darkest reaches of the occult.