You suggest a course of activity—described in no more than 25 words—to one creature you can see within range that can hear and understand you. The suggestion must sound achievable and not involve anything that would obviously deal damage to the target or its allies. For example, you could say, “Fetch the key to the cult’s treasure vault, and give the key to me.” Or you could say, “Stop fighting, leave this library peacefully, and don’t return.”
The target must succeed on a Wisdom saving throw or have the Charmed condition for the duration or until you or your allies deal damage to the target. The Charmed target pursues the suggestion to the best of its ability. The suggested activity can continue for the entire duration, but if the suggested activity can be completed in a shorter time, the spell ends for the target upon completing it.
* - (a drop of honey)
The level 4 Wizard in my campaign nearly broke the entire game with this spell. After finding out they've been working for mindflayers in the middle of the astral plane she used this spell on a CR8 Mindflayer Psionic (the lead scientist who owned the ship she snuck on) telling it to surrender the ship to her and teach her how to fly it and leave the ship with its thralls afterwards without struggle. The Mindflayer failed the savings throw, and it was so specific it caught me off guard. Afterwards she crashed it into the Labatory her allies were waiting in, and flew them all into space, now with an entire fleet of mind flayer ships chasing her. I kept throwing everything, but she kept succeeding every savings throw they threw at her, and I also had to make sure I didn't accidentally kill them. She accidentally tossed the paladin off the ship when she spun it, and eventually the rest became incapacitated by the mindflayers. But her? No, I swear she succeeded against 100 saving throws against her before she finally passed out.
Dude, this spell is overpowered.