Harry and wife Rose have become increasingly estranged so he is left feeling over the moon after she shows up from America to celebrate the fifth anniversary of the opening of the store, but seems more interested in an exciting new friendship with a female novelist. Lady Mae is surprised by her husband's unexpected arrival in London, and after hearing him blackmail his way onto a government military committee, she suspects that he's up to something sinister.

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.

After the attacks in Belgium, men are signing up to do all they can for the war effort. A chocolate sale starts in the store. Agnes has to say an emotional goodbye.

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.

Police swarm the store as Frank walks Kitty to work. Rose and Gordon find the police inside their home as well. Victor tells A concerned Agnes to go to see Henri at the police station. Henri tells her he was in Germany for personal reasons looking for his ex-love Valerie. Agnes talks to Grove and insists to him that Henri is no spy. Rose feels perturbed that she can't get in touch with Harry in Paris and finds a letter addressed to him with a detailed list of German manufacturers and addresses.

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.

Having endured a scandal in the press and dealt with Henri's arrest, Harry is determined to get the store back on track and asks Delphine to organise a special event, but takes a risk by inviting notorious American journalist Winifred Bonfils Black. Meanwhile, as Miss Mardle experiences true happiness, Agnes doubts she has made the right choice, and Lady Mae and Frank unite to help Mr Selfridge, but could there be more trouble on the horizon?.

There is a party held at the Selfridge house with everyone in high spirits. Florian thinks about what he might have done to Miss Mardle as she won't open up to him but she knows that they have no future. Agnes and Victor enjoy a walk into work together as they get ready to tell Harry that they're handing in their notice as they'll be getting married soon. Henri has being given the all clear and he's a free man. Agnes goes to see Henri for one last time.