Mr Selfridge newcomer Sean Teale has revealed the outbreak of the war is set to have a big effect on the show.
Skins star Sean, who joins the ITV period drama as Franco Colleano, the cousin of Trystan Gravelle's character Victor, told how the series picks up four years on, as World War I is about to break out, which will have repercussions for all the staff at the department store.
He explained: "The war has a very, very large effect on the store... man power, materials... that's going to affect the store hugely, and the store has quite a large staff, quite a large male staff, so it's going to have a large effect on the store and the show.
"But whether or not people come back, or go in the first place, I will leave to the imagination. There's a shift, for sure. There's twists, for sure."
Talking about his new screen alter ego, Sean said: "Franco comes in and puts a strain on some of the things Victor has going for him. He requires Victor to reign him in a bit because he's young and naturally his confidence comes through, and he's perhaps inappropriate at points.
"[For love interests], there's no doubt he's chasing at least. But perhaps the strain of the time, 1914, might play a part in whether or not that works.
"Being of Italian descent is going to add some sort of dynamic, although Victor and Franco are London-born-and-bred. One of the lines is, 'I'm as English as the next man.'"
Sean also admitted that he had been daunted joining the second series of the ITV programme as it is already so popular.
But he said there were benefits to being late to the cast: "The show's second season gets bigger, it gets bolder, it gets a little bit louder, so it's nice that I got to join then as opposed to worrying about whether it was ever going to make it in the first place."
Mr Selfridge returns to ITV on January 19.