In London, 1908, Agnes Tower, who works at Gamages department store, finds her life about to change following an encounter with Harry Gordon Selfridge. He is finalising his great plans for the biggest and finest department store the world has ever seen in Oxford Street. His family also show up in London from Chicago. Word about the impending store opening begins to spread around London, and Agnes approaches Harry for a job. He remembers her, and agrees to give her a job. Opening day is a great success, attracting huge crowds but the takings are not brilliant.

The store has now been open for a few months and the displays are still as seductive as on opening day, and the staff are poised for action. The only thing the store is missing though is customers. Harry is confident though on the outside but privately he is worried. He goes to the country with Frank, where they wait in a field and then a flying machine emerges from the clouds and flies overheard. Harry manages to secures it for a grand exhibition in store.

Harry and Ellen are enjoying their new love affair and dance into the night at an apartment that Harry has got Ellen. She ends up talking about her father and reveals that her real name is Joyce. Agnes's nasty drunk father called Reg has been fired from his job and he ends up losing his temper with his daughter, hitting her across the face.

Harry scores something of a coup when prima ballerina Anna Pavlova agrees to pay Selfridges a visit. However, Agnes's job looks to be under threat when a violent Reg reaches breaking point and gatecrashes the event - and things only get worse when Ellen invites herself along. Meanwhile, one of the department store's most loyal employees is caught stealing, a formidable new head of fashion arrives and Rose reveals her true identity to Roddy.

Harry delights in a new car brought in for a window display, but after a confrontation with Rose, who has received a visit from his mistress Ellen Love, he hits rock bottom, drinking and reliving a traumatic childhood memory as he drives the vehicle into the night. Meanwhile, Agnes falls out with Victor when she returns to Selfridges, although Henri is pleased to see her again.

Harry is left unconscious after the car accident and as his family gathers by his bedside, the news arrives that Mrs Grove is dead - something which leaves Miss Mardle confused. Meanwhile, a suffragette demonstration in the area sees all the store's staff pulling together, and as Victor and Lady Mae conduct their secret affair, Agnes and Henri's friendship continues to grow.

Author and spiritualist Arthur Conan Doyle is in Selfridges for a Sherlock Holmes book signing when he persuades Harry to hold a seance in the store - and the results of the gathering force the retail magnate to have a long-overdue heart-to-heart with Lois. Meanwhile, Agnes is transferred to women's fashion, Doris resolves to help an old friend, Miss Mardle is still agonising over Mr Grove, and Kitty has a secret admirer.

Harry and Rose are getting ready to host a dinner in honour of friends Frank and Jennie Woolworth. Frank is a fellow American retail tycoon and founder of the famous High Street chain. A Woolworth’s store is about to open in Brixton, and when Frank thinks of a possible West End branch, Harry’s feathers soon become ruffled. Lady Mae wants to introduce young Rosalie to some eligible young Society men. Kitty and Doris vie for the vacant position of Senior Assistant in Accessories and are interviewed by Mr Grove. Ellen Love makes a surprise visit to the Palm Court, with Tony Travers on her arm. Victor has a proposition for Lady Mae.

Antarctic explorer Ernest Shackleton arrives to give a lecture at the store. On the same day, the underground is shutdown when a body is discovered on the tracks, resulting in the late arrival of several employees. The identity of the body sends a wave a shock throughout the store. Meanwhile, Frank Edwards is disappointed when he needs a favor, and Roddy Temple's presence continues to cause problems.

Lady Mae arranges an after hours shopping spree for King Edward VII. To thank Harry, the King invites the Selfridges to the opening of Ellen Love's new play, much to Rose's dismay. The Selfridges and Lady Mae discover the play is a satire aimed at ridiculing them, and scripted by an embittered Frank Edwards. Ashamed and humiliated, Rose takes the children back to America. Meanwhile, wedding bells will soon be ringing for two of Selfridges' own.

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.

After recent ructions, Harry is more determined than ever to get Selfridges back on track and asks Delphine to organise a special event in the store.

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.