Like its elite counterpart, Invoke Lightning, this skill checks for enchantment upon completion of the cast, rather than at the start of it. This means that if you are enchanted when you begin casting but are no longer enchanted when you finish, you will suffer exhaustion. The reverse is also true. It also means that you can cancel this spell, or be interrupted, without suffering exhaustion.
The third foe struck must be nearby to the second foe rather than the first.