I have a question about last Thursday's episode. In fact, it's a time-honored question that several editions of D&D have answered differently:

Can you counterspell... counterspell?

Yes, you can as long as the caster abides by Counterspell's limitations.

You keep repeating the cycle over and over and over aslong you meet the spells requirement.

Quote from Brian_Avery >>

But also, if the original caster, say of a fireball spell had someone try to counterspell the fireball and the original caster of that fireball tried to use counterspell to stop the counterspell of his fireball... then he would still lose the fireball spell as he would have to abandon casting it to cast counterspell against the counterspell targeting his fireball.

This would happen each and every time no matter what the original spell was, as it has to be abandoned to cast counterspell against the counterspell targeting the original spell.

Per the Sage Advice Compendium, that is not correct. 

They specifically state that someone casting Fireball (or any spell, really) CAN counterspell a counterspell and successfully cast Fireball (or whatever spell it is) during the same turn.

This is a link on the topic:
http://dnd.wizards.com/articles/sage-advice/ability-check
See the part under "Is there a limit on the number of spells you can cast on your turn?". It specifically mentions multiple spells per turn and an example of counterspelling counterspell.