With the Bug-Bear finally locked back up in Tartarus where it belongs, former special agent Sweetie Drops finds herself feeling truly at peace for the first time in the four years since she went into hiding. With her crush best friend Lyra now aware of her true identity, she feels like she can really begin enjoying her new life as Bon Bon, resident candy maker of Ponyville.

That is, until she is summoned by the Princesses the day after Cranky and Matilda's wedding.

Now that the threat that caused it to be shut down in the first place is gone, Celestia wants to start back up her secret anti-monster organization…with Sweetie Drops as its new leader. Despite some painful memories, Sweetie Drops cannot deny that she misses the good she used to do as an agent, and she eventually accepts - but on the condition that she decides which ponies join her new team, leading her to assemble a mix of old friends and new faces, including some of her fellow Ponyville residents.

Look out all evil creatures of the world.

D.E.F.R.O.S.T. is back in action.