Murdoch and Crabtree investigate the strange murder of Henri Gaston, who is found lying in the upper limbs of a very tall tree. There were no footprints leading up to tree so they have no theories as to how he may have gotten there. Gaston was an avid astronomer with a particular fascination about Mars and Constable Crabtree begins to think that Martians may be responsible. Murdoch however suspects a more human perpetrator, especially when he learns that Gaston was refusing to sell his land to a developer. What they eventually stumble upon is something that is completely alien to their experience.