On a lazy afternoon of witty repartee, Lucien (Lucifer?) Gregory reveals to the poet Gabriel (angel?) Syme, that he is an anarchist (anti-christ?). The pair go, quite literally, underground (Hades?) and double-bluff each other as to who is anarchist and who is policeman.
Is this allegory, satire or, as the title implies, a 'Nightmare' involving Lucien and Gabriel as 'the two fantastics'? To support the latter there is a prolonged 'nightmarish' chase section where the protagonists oten ask each other, 'When will I wake up?'
The main body of the 'crime' element of the novel involves a helter-skelter puruit of the anarchists across Edwardian England and northern France. This is coupled with the test of Gabriel and Lucien's 'my word is my bond' in a web of betrayal and deceit.
Mr Chesterton has a distinct style which is especially demanding at the start of the novel but it progresses to an easier ride as he concentrates on the narrative rather than descriptive. This novel is difficult to classify and open to multiple interpretations. Quite challenging. No sooner had I pigeon-holed the novel than it made a fool of me.