The plot concerning advanced regeneration research puts this novel in the science fiction genre, but it could also be described as a mystery thriller.
The plot centers on a young marine biology student named Adam Eddington, who travels to the remote island Gaea off the coast of Portugal for a summer job working for a famous scientist, Dr. O'Keefe.
Even before he leaves JFK airport, Adam is approached by Carolyn ("Kali") Cutter, the beautiful, well-traveled daughter of a rich American industrialist living in Europe.
Adam's attempt to do so makes it nearly impossible to pass on the real papers, hampered as he is by Kali's presence and spies from both sides.
Intelligent, principled and a bit naive, 16-year-old Adam Eddington is a biology major who has been interning at Woods Hole, Massachusetts in the summers, until "Old Doc" Didymus sends him to work with Calvin O'Keefe instead.
The Arm of the Starfish is Poly's first appearance, as such, but Meg Murry O'Keefe was pregnant with her at the time of A Swiftly Tilting Planet.
In later books, Poly begins to spell her name Polly to avoid awkward explanations about being named after Polyhymnia, the Greek muse of sacred music, and to keep people from pronouncing it with a long o. Charles O'Keefe is Poly's eldest younger brother, the closest to her in both age and companionship.
Canon Tallis is a bald clergyman with no eyebrows, said to have lost his hair due to withstanding torture in the Korean War.
Brusque and incisive, and not at all pious by L'Engle's definition, he defies the conventional image of a priest, and seems more than a little sinister to Adam at first.
Calvin first appeared in A Wrinkle in Time, as a 14-year-old high school junior, a popular and athletic but neglected adolescent from a family with eleven children.
As of The Arm of the Starfish, she is a scientist and mathematician (albeit without a doctorate) who assists her girlhood friend and husband Calvin with his work, while also helping to raise her large family.
The surname of the duplicitous Dr. Eliphaz Ball is initially misunderstood by Adam as Baal, a name given to a number of deities considered "false gods" by the Hebrews in ancient times.
"[1] Robert Hood wrote in The New York Times, "Tense, tricky, well-plotted, 'The Arm of the Starfish' has all the stuff of which adult spy novels are made.
The Arm of the Starfish takes place about twelve to thirteen years after the events of A Swiftly Tilting Planet, the last of the Time Quartet of books about the Murry family.
However, L'Engle's use of the term Kairos (which she describes inside the front cover of Many Waters as "real time, pure numbers with no measurement") suggests a religious connotation as well.
Adam Eddington meets Vicky Austin the following summer in A Ring of Endless Light, and Meg and Charles Wallace are mentioned in The Moon by Night.