Five years since the store's opening, business is booming for Harry and new faces have joined old favourites at Selfridge's. Rose makes a surprise return home with a mysterious new friend in tow, Lady Mae is forced to deal with troublesome husband Lord Loxley who arrives in town from the country, and Agnes returns from a creative secondment in Paris - but is Victor pleased to see her?

Rumblings of war and social unrest inspire trades union activists to target Selfridge's. Harry responds by throwing a tango party to thank the staff for their hard work. He also wants to do something more public and asks Agnes to organise a Celebration of Empire in the store - but is it too much for her? Meanwhile, Rose secretly seeks out an old friend for Harry, and trouble is brewing for Lady Mae.

Agnes is working through the night getting ready for the Empire Exhibition that Harry is rolling out across the store. Mr Crabb attempts to cover for Mr Grove after Harry thinks that he’s late for work again. Harry receives a visit from Henri and takes the opportunity to apologise and asks him to return to work. Gordon is fed up with the frostiness between his parents. Miss Mardle asks Grove to meet her at her new address and he finds out that she has inherited a beautiful London home and income from her brother. Lady Mae manages to find out that truth about Loxley’s finances and discovers that he has gambling debts and is rumoured to be all washed up.

With news of the first horrors of war in Belgium, the men of Selfridges clamour to sign up, while Rose, Delphine and Lady Mae organise a special chocolate sale to aid refugees - which goes down a treat in the store and proves inspirational for Miss Mardle. Thackeray suspects Henri is up to no good, Victor faces a family crisis and Loxley gets his shady money-making plans off the ground.

With so many of the men signing up for duty, the women are now working in the loading bay and struggling to adjust, while Harry yearns to do more for the war effort, so Delphine introduces him to several senior government figures who could help. Crabb organises rifle training for the staff, Thackeray's anxieties about Henri reach a new level and Miss Mardle entertains a surprising house guest. Lord Loxley suddenly seems to be in the money, much to Lady Mae's concern.

With German goods being taken off the store's shelves, Harry organises a patriotic concert to raise money for British troops, and Lady Mae arranges for an old friend to headline the event. However, Harry has also offered to help the government, and just as the gig is about to begin, he's ordered to leave London on a secret mission to Berlin. Elsewhere, Agnes and Victor find themselves going over old territory and an increasingly paranoid Thackeray takes action against Henri.

Following Henri's arrest and Harry's disappearance, everyone is in a state of confusion and the police arrive at the Selfridges' home in search of clues. However, when Rose discovers her husband is away on secret government business, she's more worried for his safety than ever before. Meanwhile, Agnes receives an ominous telegram, Lady Mae has to make a tough decision, and will Loxley get his comeuppance?

Harry deals with a raft of problems on his return from his secret government assignment - not least the news of Henri's arrest. Coming to his employee's aid, Mr Selfridge pulls a few strings and calls in a favour to get him out of custody. Meanwhile, the beleaguered staff receive a much-needed morale boost when Delphine arrives at the store accompanied by Hollywood producers and actresses, and Lady Mae decides it's high time she cut her ties with Loxley.

Harry is desperate to clear his name, Victor and Agnes endure some painful soul-searching when a loved one returns, and Miss Mardle grapples with a romantic dilemma.