Leading Strike is a 1st level avenger At-Will attack that was introduced in Divine Power.
Leading Strike
Avenger Attack 1
You show an ally how to hit your foe where it hurts.
Melee weapon
Target: One creature
Attack: Wisdom vs. AC
Hit: 1[W] + Wisdom modifier damage. One ally adjacent to you or to the target gains a bonus to his or her next damage roll against the target equal to your Intelligence modifier.
Level 21: 2[W] + Wisdom modifier damage.