The user drains life from a foe within a 20 foot radius around the user. The foe is drained of 1d6 hit points of necrotic damage. Every odd level (3rd, 5th, 7th, etc.) the caster is able to target an additional foe and consequentially an additional 1d6 of damage.
At 7th level, the caster learns to channel the drained damage to heal himself/herself, and with a successful CHA check the user receives 50% of the base rolled damage total in hit points as healing.
Example: a 7th level warlock is surrounded by five orcs within a 20' radius and casts the spell. It affects three of the orcs (1 for 3rd, 5th and 7th levels), and rolls 14 points of necrotic damage against them on 3d6. The user rolls a successful CHA check and seven of the 14 points are gained in hit points (not to exceed max HP) that round.