Attacking, Journeys in the Dark
I - Rules
(see JITD, p. 19)
If a hero has two one-handed Melee weapons equipped at once, he may gain the benefits of an Off-Hand Bonus. The weapon the hero does not use to attack adds its off-hand bonus to attacks with the other weapon.
Example: A hero has a sword and a dagger equipped and attacks with the sword. The hero’s attack gains the dagger’s offhand bonus, which is one free surge. The hero makes his attack with the sword normally and adds the free surge from the offhand bonus to the result.