As part of the action used to cast this spell, you must make a melee attack with a weapon against one creature within the spell’s range, otherwise the spell fails. On a hit, the target suffers the attack’s normal effects, and in addition  lightning leaps from the target to all creatures of your choice that you can see within a 15 ft sphere of it. The creatures must make a constitution saving throw or take 1d4 lightning damage.

This spell’s damage increases when you reach higher levels. At 5th level, both the melee attack deals an extra 1d4 lightning damage to the target, and the lightning damage to the other creatures increases to 1d4 + your spellcasting ability modifier. Both damage rolls increase by 1d4 at 11th level and 17th level.