13 Moons: Legacy of the Guardians

For three years, Sean Murphy has led his coven in relative peace, honing their magical skills and deepening his bond with his powerful girlfriend, Katie. This tranquility shatters when a sense of profound wrongness returns to their small South Carolina town. After the sudden, peaceful death of his grandfather, Tom, Sean inherits the full weight of his family's legacy. He learns they are not just witches, but part of a long line of "Guardians" who protect the world from Malevolent Spirits.
His grandfather leaves him a cryptic warning and a powerful, dangerous artifact called a Wayfinder. The threat reveals itself in the form of Alistair Finch, a charismatic tech billionaire whose "Aethelgard Institute" is a front for a terrifying plan. Finch, possessed by a powerful Keystone Spirit, intends to use a geothermal facility built on a magical nexus to perform a ritual during an upcoming solar eclipse.
This ritual will not just free other spirits, but will tear open the Gates between dimensions, allowing ancient, cosmic "Outer Gods" to consume reality. To find a way to stop the ritual, Sean is forced to use the Wayfinder, a scrying tool that burns away the user's life force as fuel. The vision it grants him comes at a great personal cost, leaving a permanent silver streak in his hair but revealing the date and nature of the ritual.
The coven, now joined by an experienced witch named Sam and guided by Sean's estranged, non-magical uncle, Todd, splits into two teams. Katie leads a subterfuge mission to disrupt Finch's human operations, while Sean's team focuses on finding a way to dismantle the magical wards at the nexus site. The final battle takes place on the day of the eclipse. The coven launches a desperate, two-front assault, freeing Finch's enthralled followers while battling the ritual's powerful magical defenses.
In a final, desperate gambit, Sean and Katie fuse their consciousnesses and project to the astral plane to fight the Spirit's true form. They succeed in destroying the entity, but the victory is not without a terrible price. Their friend Matthew is gravely wounded, and they discover that their victory was so powerful it acted as a flare, alerting even older, more dangerous entities to their existence.
The story ends with the coven, though wounded and grieving the loss of their leader, embracing their true calling as Gatekeepers. Led by Katie, they set their sights on a new mission, understanding that their war is far from over and that their duty is to protect all the Gates, beginning with a failing one in Ireland.