I can't seem to find an answer (probably because it's rare), but can a creature be under the spell "Suggestion" from multiple sources at the same time? What if the two suggestions are contradictory?

From the PHB

Combining Magical Effects

The effects of different spells add together while the durations of those spells overlap. The effects of the same spell cast multiple times don't combine, however. Instead, the most potent effect — such as the highest bonus — from those castings applies while their durations overlap, or the most recent effect applies if the castings are equally potent and their durations overlap.

For example, if two clerics cast bless on the same target, that character gains the spell's benefit only once; he or she doesn't get to roll two bonus dice.

To clarify: second suggest will override first until completed and then ends. If first is still in effect by duration, they would then have to do that if still possible.

Example 1:  Enemy A casts Suggestion on you to exit the castle and run back to the village. Duration is 8 hours.

Example 2: Enemy B then casts Suggestion on you to head further into the castle into the prison room where a friendly NPC is held and hand them a potion of healing which Enemy B gives you (it's actually poison but you don't know that). Duration 8 hours.

How it resolves:

Enemy B's suggest is more recent, so you do that first. You would head to the prison and hand over the vial to the NPC. Enemy B's suggestion has finished, so the spell ends. Enemy A's spell is still in effect so now you follow that suggestion and immediately head back to the village. On reaching the village the suggestion ends. Not only do you then realise you've wasted time, you might find the prisoner NPC you were meant to save is now dead from the poison you gave them.

Thanks for the replies. This clarifies a lot.