You fire a ray of fiery energy from the ruby (which is the material component for the spell) at a target, rolling a ranged spell attack to see if this hits. On a successful hit, the beam locks onto the target. When this initially hits and at the start of the target's turns for the duration, it takes 1d4 fire damage (increases to 2d4 at level 5, 3d4 at level 11, and 4d4 at level 17). If the target moves more than 120 feet away from you or you lose concentration, the spell ends.