In the wake of a joyful wedding between his best friend White Lance and his beautiful new wife, former guard captain Shining Armour receives another reason to celebrate: the Deer of the forest realm of Cervidas want peace after nearly four decades of hostility, and the Crystal Prince and Princess will act as Equestria's emissaries.

But as the pony ambassadors arrive in the Deer capital of Concordia, a brilliant villain awaits - harbouring a cruel secret that could lead to the destruction of not just Equestria, but half the known world. Shining Armour and Princess Cadence will face their greatest challenge yet in the cold snowlands of Cervidas...