What is the name of this book?
The story starts with a worker who accidentally gets a pick-axe or metal spike lodged into his head and starts seeing or sensing strange things. A scientist/doctor investigates and determines that the metal inserted into his brain enables extra-sensory perception. The scientist/doctor (and a friend?) decide to intentionally insert a piece of metal into their own brains to replicate the effect. They become aware of massive and ancient telepathic alien/monster beings on Earth who notice them too and now they're in trouble and have to warn the world.