The poem is a description of a villainous character, Macavity, a criminal who is so skilled in committing crime, that no one can ever find him. For whenever they reach the crime scene, he's not there.
Macavity is called the 'mystery cat' and the 'hidden paw' because he is a great criminal. He's defied many laws and has baffled the Scotland Yard and the Flying Squad.
The poet believes that there is no one like Macavity, for there is no rule open could think of that he has not broken. He has managed to challenges even the laws of nature, as he can float in the air without any support. One may look for him in the basement or in the sky, but one thing that is for sure is that he would never be found.
Macavity is also called the ginger cat. He is very tall and thin. It is not very difficult to recognise him, as he has very sunken eyes. His eyebrows are deeply lined because of constant plotting and strategising. He could also be recognised by sheer self-neglect. His coat is dusty and his whiskers are uncombed. He would move his head from side to side like a snake. And when you think he’s sleeping, he’s merely pretending. He is actually alert all the time.
There is just no one like Macavity. He is actually a devil inhabiting a cat’s body. One may meet him here or there, but on the crime scene, he would never be there.