Rainbow Dash has been enduring bizarre aches and pains for the past few days, and she isn't sure why - though it may be because of everypony's strange behavior around town lately.
Twilight accidentally turns her friends into foals - including her - and Pinkie has to take care of them all before they wreak havoc on SugarCube Corner.
When a possibly-harmless venture into the Everfree Forest turns deadly, Rainbow Dash is stricken down with a disease, only to find out later that it's more than just ordinary... can the ponies help her in time before it gets out of hand?