The offspring of the mane 6 have grown up, and they have joined the Equestrian Royal Military as a special ops unit called the 'Descendants of Harmony'.
Night Echo (Twilight's firstborn son) and his team are called to scout out a area of magical 'disturbances' in the middle of the Everfree Forest, but to find out that an old enemy is lying in wait for them instead.

(This story is based in a future setting, and things HAVE changed in Equestria in this Fic)