It's 1920, and Christmas is coming. Major Lennox finds a body on his doorstep - why on his doorstep? Was it to do with the Countess? Was it about the ruby necklace? Lennox goes to Melrose Court, home to his uncle, Lord Melrose, to uncover the mystery. But then, the murders begin, and it snows, and it all becomes very complicated.

June 1933. Independent, young Kitty Underhay has been left in charge of her family’s hotel, The Dolphin, on the tranquil English coast. But when several rooms are broken into and searched, including Kitty’s own, she quickly realizes that something out of the ordinary is afoot at the hotel. Soon, rumors are flying in the cozy town that someone is on the hunt for a stolen ruby. A ruby that Kitty’s mother may well have possessed when she herself went missing during the Great War.

Lady Emily Hardcastle is an eccentric widow with a secret past. Florence Armstrong, her maid and confidante, is an expert in martial arts. The year is 1908 and they've just moved from London to the country, hoping for a quiet life. But it is not long before Lady Hardcastle is forced out of her self-imposed retirement. There's a dead body in the woods, and the police are on the wrong scent. Lady Hardcastle makes some enquiries of her own, and it seems she knows a surprising amount about crime investigation...

London, 1925. With their band the Dizzy Heights, jazz musicians Ivor ‘Skins’ Maloney and Bartholomew ‘Barty’ Dunn are used to improvising as they play the Charleston for flappers and toffs, but things are about to take a surprising turn. 

At the end of her first unsuccessful season out in society, Lady Georgiana has all but given up on attracting a suitable man - until she receives an invitation to a masked Halloween ball at Broxley Manor. Georgie is uncertain why she was invited, until she learns that the royal family intends to marry her off to a foreign prince, one reputed to be mad.

It is the early spring of 2016, and Queen Elizabeth is at Windsor Castle in advance of her 90th birthday celebrations. But the preparations are interrupted when a guest is found dead in one of the Castle bedrooms. The scene suggests the young Russian pianist strangled himself, but a badly tied knot leads MI5 to suspect foul play was involved. The queen leaves the investigation to the professionals - until their suspicions point them in the wrong direction.

Sussex, England, 1929. Mydworth is a sleepy English market town just 50 miles from London. But things are about to liven up there, when young and handsome Sir Harry Mortimer returns home from his diplomatic posting in Cairo, with his beautiful and unconventional American wife, Kat. No sooner have the two arrived, when a jewel robbery occurs at Harry's aunt's home - Mydworth Manor. The police are baffled and overwhelmed with the case. But Harry and Kat have an edge in the hunt for the dangerous culprit.

Evelyn Christie has resigned herself to another long, boring weekend at Hessleham Hall, the home of her husband, Tommy's, family. However, it turns out to be anything but dull when his uncle, the Earl of Northmoor, is shockingly murdered! Evelyn must use all of her sleuthing knowledge, gained whilst she was a member of the Police force during the war, to find out who the murderer is before the bungling local police force decide the Earl was bumped off so Tommy could inherit his title.

London, 1923. Olive Belgrave needs a job. Despite her aristocratic upbringing, she’s penniless. Determined to support herself, she jumps at an unconventional job - looking into the background of her cousin’s fiancé, Alfred. Alfred burst into the upper crust world of London’s high society, but his answers to questions about his past are decidedly vague. Before Olive can gather more than the basics, a murder occurs at a posh party. Suddenly, every Bright Young Person in attendance is a suspect, and Olive must race to find the culprit.

In a peaceful retirement village, four unlikely friends meet up once a week to investigate unsolved killings. But when a local property developer shows up dead, 'The Thursday Murder Club' finds themselves in the middle of their first live case. The four friends, Elizabeth, Joyce, Ibrahim and Ron, might be octogenarians, but they still have a few tricks up their sleeves. Can our unorthodox but brilliant gang catch the killer, before it's too late?