After the rich Lord Lebanon has been strangled, a group of different characters assembles at Mark's Priory, his lonely manor in the north of Scotland, to attend the reading of his will. However, as lawyer Frank Tanner explains—in reading a "second-to-last-will"—to the potential heirs, they will first have to stay together at the manor for six days and six nights. Thinking that Lebanon has died of heart failure they all agree. It turns out to be a dangerous requirement as the manor is cut off from the outside world by a storm and one by one the visitors are murdered—strangled with an Indian scarf. In the end, of all the guests, family and staff only Tanner, Isla Harris and Bonwit the butler survive. The last will is read and it is revealed that Lord Lebanon has in fact left all his money to the man he considered to be the greatest of the century: Edgar Wallace.
The ruins of Fossoway Abbey are supposed to conceal the legendary treasure of the Chelford family, sought by Harry Chelford, last of his line, with fanatical zeal. Due to a hereditary disease, he is liable to fall victim to insanity at any time. His fiancee, Leslie Gine, is more attracted to Dick Alford, Harry's cousin and steward at Chelford Manor. Meanwhile, her brother Arthur, a London lawyer is being blackmailed by his chief clerk Gilder, who wants Leslie for himself. Gilder has purchased some bills of exchange on which Arthur forged the signature of Lord Chelford to pay for his own gambling debts. There is also the 'Black Abbot', a mysterious figure who is seen moving about in the old ruin and supposedly guards the treasure. Inspector Puddler of Scotland Yard and his assistant Horatio are called in when a man is found stabbed to death and they try to solve the mystery. Among the suspects is the butler Fortuna who Puddler recognizes as a former inmate of Dartmoor prison. Mary Wenner, who used to be secretary of Lord Chelford (and an aspirant to become his wife), joins forces with Gilder to find the treasure. They manage to discover some scroll cases containing maps of the abbey but are driven off by the Black Abbot. They later return to find the maps gone. Wenner is shot and killed by Arthur Gine, who himself is later killed in a confrontation with Gilder. Leslie Gine calls off the wedding with Lord Chelford. Lord Chelford, plagued by his deteriorating sanity completely loses his grip on reality when he encounters his mother (whom he believes to be dead) in the grounds of the manor. Lord Chelford shoots his mother and the Black Abbot, takes Leslie as a hostage and hides with her in the tunnels beneath the abbey after also killing Gilder. It turns out there have been two Black Abbots: one was the butler working as an agent for Gilder, the other was Alford, working with the family doctor Loxon to care for the insane Lady Chelford whom they had kept hidden from her son. There is a shoot-out with the police and Lord Chelford is killed by a cave-in. Among the stones falling on the last Lord Chelford are some chests that contain the treasure.
Both Scotland Yard and the criminal community of London are trying to discover the identity of "the Squealer". This mysterious fence forces criminals to sell him their wares for a pittance. When some object, he "squeals" to the police. Those who oppose him are ruthlessly killed, preferably by means of the poison of the Black Mamba. Inspector Elford of Scotland Yard investigates and he has plenty of suspects. The trail leads to the strange Mr. Sutton, owner of a zoological store that also carries predators and poisonous snakes. During his investigation, Elford meets Mrs. Mulford, an older lady who tries to help ex-convicts, and Beryl, her niece, who writes crime stories and works as a court reporter. Inspector Elford discovers a similarity between the typeset of a machine also used by Sutton and letters written by the Squealer. To make Sutton confess, he is tricked by Mrs. Mulford in cooperation with the police into drinking what he believes to be poisoned tea.
Sir John, le chef de Scotland Yard, est perplexe. Deux personnes ont été assassinées, sans qu'à première vue il y ait un lien entre elles. L'inspecteur Dick Martin et son assistant Holmes s'occupent de l'enquête. Ils tombent sur Pheeny, un malfrat, qui raconte à Martin une histoire étrange d'une porte aux sept serrures qu'il aurait fracturé pour un commanditaire inconnu. Pheeny est retrouvé tué peu après, Martin reçoit le blason d'une famille que Pheeny lui a envoyé juste avant sa mort.
Un homme est retrouvé assassiné sur la Tamise, l'arme du crime est un fusil-harpon, signature du mystérieux « requin » que Scotland Yard traque sans succès.
Un gang mystérieux exige de certains riches londoniens qu'ils payent de fortes sommes en échange de leur sécurité et leur recommande de ne pas se tourner ves Scotland Yard, sous peine d'y perdre la vie. Certains téméraires bravent la menace et en meurent dans la nuit même. L'inspecteur Weston et son collègue Tetley subodorent là des méthodes américaines et font appel à un homme du FBI, Allerman...
Le Dr. Lilli König est psychothérapeute. Sa vie amoureuse est un désastre à cause de ses propres peurs et névroses. Lorsqu'un jour une patiente, la jeune Pauline, arrive, elle affirme que son compagnon actuel ne lui convient pas, Lilli tient qu'il vaudrait mieux qu'ils se séparent. Révolté par ce conseil, le compagnon, le célèbre photographe de mode Martin Bohlen, un réputé coureur de jupons, cherche Lilli König et fait semblant d'être un nouveau patient.
Grande alerte dans la police de Londres : un meurtrier manifestement fou a tué trois jeunes femmes en très peu de temps. À chaque fois, le délinquant laisse un bouquet de narcisses jaunes sur les lieux du crime. L'inspecteur en chef Whiteside prend en charge l'enquête. Cependant, Jack Tarling, agent d'une compagnie aérienne internationale, et le mystérieux Chinois Ling Chu ne croient pas en l'action d'un individu. Surtout pas quand ils viennent d'échapper à un attentat à la bombe qui a détruit une cargaison d'héroïne de contrebande qui venait d'être découverte.
During a guided tour of Garre Castle, a man is killed by an arrow after sneaking away from the rest of the group. Shortly thereafter, Mr Howett and his adopted daughter, Valerie, move into Lady's Manor, next door to the castle. Valerie is looking for her mother she has not seen in 20 years. John Wood, a friend of Valerie's brother John Bellamy, who was killed in the war, is also there.
Sur fond d'efficaces faux-monnayeurs, un jeune homme dont le père est en fait un malade mental, se soupçonne lui-même, dans de fortes crises amnésiques, d'être l'auteur de moult méfaits, ce qui arrange bien sûr les affaires criminelles du véritable malfrat .....
Le marin Peter Hille avait hâte de passer ses vacances de Noël avec son épouse Hanna depuis longtemps. Mais lorsqu'il débarque à Copenhague, il est déçu qu'elle ne l'attende pas. Heureusement, il y a une place disponible à la capitainerie. Cependant, il doit partager sa chambre avec le chauffeur Valdemar Olsen. Il est en train de gagner sa vie en tant que chanteur, mais il vit principalement de la contrebande de cigarettes.