Magic Resistance

The ability of Dwarves, Battle Dwarves and Crystal Dragons to completely resist a spell aimed at them.

This does not stop area effect, mass spells or a Chain Lightning that already has begun leaping from affecting other creatures, even if they are aimed at the creatures.

The ability can be gained or improved through the Secondary Skill Resistance (cumulative with the Magic Resistance artifacts), or by standing next to a Unicorn or War Unicorn

As suggested above if Chain Lightning is resisted by the first creature then the spell is stopped completely.