Although Dief couldn't be there, Zach did another episode at his house with Henry, Sutton and Oli, who was definitely not on D of E and just there as a pre-recorded sounds board.
Zach refuses to admit that the reason Dief wasn't in it is because he refuses to disclose to him the location of his house.
Anyway, this was after watching an episode of Doctor Who, so they discuss that, as well as playing the train game and constantly reminding us that Oli is in fact present for the recording ;)