Question: Death at the Dolphin is a detective novel by Ngaio Marsh; it is the twenty-fourth novel to feature Roderick Alleyn, and was first published in 1967, the plot centers on a glove once owned by Hamnet Shakespeare, Hamnet  was the only son of William Shakespeare and Anne Hathaway, and the fraternal twin of who?

Context articles: Spinsters in Jeopardy
Hamnet Shakespeare
Vintage Murder
Death at the Dolphin
Enter a Murderer
Last Ditch
A Man Lay Dead
Light Thickens
Died in the Wool
Colour Scheme

Spinsters in Jeopardy is a detective novel by Ngaio Marsh; it is the seventeenth novel to feature Roderick Alleyn, and was first published in 1954.
 The novel takes place in the countryside of France, where Alleyn is vacationing with Agatha Troy, now his wife, and their son Ricky; it concerns an unusual and sinister plot which is perpetrated against traveling spinsters.
Hamnet Shakespeare (baptised 2 February 1585 – buried 11 August 1596) was the only son of William Shakespeare and Anne Hathaway, and the fraternal twin of Judith Shakespeare.
 He died at age 11.
 Some Shakespearean scholars speculate on the relationship between Hamnet and his father's later play "Hamlet", as well as on possible connections between Hamnet's death and the writing of "King John", "Romeo and Juliet", "Julius Caesar", and "Twelfth Night".
Vintage Murder is a detective novel by Ngaio Marsh; it is the fifth novel to feature Roderick Alleyn, and was first published in 1937.
 The plot centers on a traveling theatrical troupe in New Zealand.
 One of the cast members was a minor character in "Enter a Murderer", and refers to that case early in the story.
Death at the Dolphin is a detective novel by Ngaio Marsh; it is the twenty-fourth novel to feature Roderick Alleyn, and was first published in 1967.
 The plot centers on a glove once owned by Hamnet Shakespeare, on display at a newly renovated theater called the Dolphin; the novel was published as "Killer Dolphin" in the United States.
 Several characters from the novel return in Marsh's final book, "Light Thickens".
Enter a Murderer is a detective novel by Ngaio Marsh; it is the second novel to feature Roderick Alleyn, and was first published in 1935.
 The novel is the first of the theatrical novels for which Marsh was to become famous, taking its title from a line of stage direction in "Macbeth", and the plot concerns the on-stage murder of an actor who has managed to antagonize nearly every member of the cast and crew.
 Unfortunately for the murderer, Inspector Alleyn is in the audience.
Last Ditch is a detective novel by Ngaio Marsh; it is the twenty-ninth novel to feature Roderick Alleyn, and was first published in 1977.
 The plot concerns drug smuggling in the Channel Islands, and features Alleyn's son, Ricky, in a central role.
A Man Lay Dead is a detective novel by Ngaio Marsh; it is the first novel to feature Roderick Alleyn, and was first published in 1934.
 The plot concerns a murder committed during a detective game of murder at a weekend party in a country house.
 Although there is a side-plot focused on Russians, ancient weapons, and secret societies, the murder itself concerns a small group of guests at Sir Hubert Handesley's estate.
 The guests include Sir Hubert's niece (Angela North), Charles Rankin (a 46- or 47-year-old man about town), Nigel Bathgate (Charles's cousin and a gossip reporter), Rosamund Grant, and Mr and Mrs Arthur Wilde.
 Also in attendance are an art expert and a Russian butler.
 Unlike later novels, this novel is more focused on Nigel Bathgate and less so on Alleyn.
Light Thickens is a detective novel by Ngaio Marsh; it is the thirty-second, and final, novel to feature Roderick Alleyn, and was first published in 1982.
 The plot concerns the murder of the lead actor in a production of "Macbeth" in London, and the novel takes its title from a line in the play.
 A number of characters in the book appeared previously in Marsh's novel "Death at the Dolphin".
 The novel is dedicated to the actors James Laurenson and Helen Thomas who had played Macbeth and Lady Macbeth respectively in the author's 1962 production of the play, which she had previously directed, also for The Canterbury University Players, in 1946.
Died in the Wool is a detective novel by Ngaio Marsh; it is the thirteenth novel to feature Roderick Alleyn, and was first published in 1945.
 The novel concerns the murder of a New Zealand parliamentarian on a remote sheep farm on the Canterbury Region of the South Island of New Zealand, said to be located in Mackenzie country near Aoraki/Mount Cook (which in the novel is referred to as the "Cloud-Piercer", the highest in a series of several peaks surrounding the high plateau where most of the action occurs).
 Like the previous novel in the series ("Colour Scheme") the story takes place during World War II with Alleyn doing counter-espionage work.
 The format of the book is somewhat unusual, in that Alleyn does not arrive at the scene of the murder until fifteen months after it has taken place, and much of his detecting is founded upon stories told him by the chief witnesses in the case.
Colour Scheme is a detective novel by Ngaio Marsh; it is the twelfth novel to feature Roderick Alleyn, and was first published in 1943.
 The novel takes place in New Zealand during World War II; the plot involves suspected Nazi activity at a hot springs resort on the coast of New Zealand's Northland region and a gruesome murder whose solution exposes the spies.
 Alleyn himself is working for military intelligence in their counterespionage division.
 Marsh's next novel "Died in the Wool" also concerns Alleyn's counterespionage work in New Zealand.