The mage crafts a gateway into another realm and calls a spirit. Any spirit may be called, though there are some obvious reasons not to attempt to summon a greater demon or one of the gods. The target may make a saving throw, but receives a penalty equal to the caster’s level. The target spirit is under no compunction to obey the caster upon arrival.
Should the caster fail the ritual roll, it is very likely that something else will come through the portal and into the mortal realm. Good luck.
This ritual requires that the mage draw various intricate circles and signs in chalk and call out the names of the spirit which he wishes to summon. Knowing the spirit’s true name gives the caster a +5 bonus to the Intelligence test for the ritual, making him much more accurate in his summoning.