The webway – a bizarre alien landscape created by the eldar in ages long past; a network of otherworldly tunnels that burrow through time and space. When the wards protecting the webway are accidentally breached by the primarch Magnus, hordes of daemons are able to exploit this weakness to attack the heart of Terra directly. While the Emperor himself tries to hold the wards in place, a desperate battle takes place in the webway itself – a battle that requires very special combatants – among them the Psi-Titan Borealis Thoon.