The Ancient Blood series.

The seal is broken. The iron serpent tastes the air.
For thirty years, Father Richard Blood has been haunted by voices from the dark—cold, dissonant whispers that doctors called schizophrenia and the Church called a curse. Richard knows the truth: they are the voices of the damned, and they are trying to warn him.
When an impossibly deep...

The seal is broken. Now, the machine is hungry.

They thought the nightmare ended in the Syrian desert. They were wrong.
The horror that began at the ancient Temple of Moloch has found a new, industrial pulse. In the frozen, desolate wastes of the Arctic, the Abadi Group has reopened the Kola Superdeep Borehole—a Soviet-era relic that pierced the...