Maskelyne produced this assassination material. It does not come from the screenwriters or the deceased ghost writer.
Are we seriously expected to believe that Maskelyne was a government hit-man? From button compasses to button man?
Maskelyne is surely making this up. And perhaps lifting the stolen shoes idea from Conan Doyle’s Hound of the Baskervilles.
However, Maskelyne's murder method might well have worked. The lethal poison would have been drawn from the Acokanthera plant.
Neuwinger's book on African Ethnobotany has a fascinating section on Hunting Poisons:"Acokanthera could almost be called the "national poison plant" of Kenya, such is its widespread and unrivalled use. Anyone who hunts with a poisoned arrow, poisoned spear or poisoned trap and uses poisoned weapons against enemies, reaches solely for Acokanthera. Someone who wishes to get rid of a person he dislikes makes sure he can get hold of Acokanthera."
Neuwinger then lists over 30 examples of poison arrow murders in Kenya from 1964 to 1971! (Maskelyne probably read or heard about some of these cases.)

"Acokanthera arrow poisons, kept in a dry place, will keep their effect for decades. Death occurs in all warmblooded animals after a few minutes with the same symptoms: fibrillary twitching of the neck and chest musculature, repiratory distress, increased and irregular heart beat, strong rise in blood pressure, clonic and tonic convulsions of differing degree, most severe dyspnoea accompanied by wheezing, clicking and gasping rattling, typical in cardiac poisoning...and finally cardiac arrest." Neuwinger