Margery Allingham 
Hide My Eyes [EPUB ebook] 

The arrival of the ’bus was timed to perfection. Nobody of the slightest importance saw it at all. Traffic was slack, the theatres were only halfway through the evening performances, and no police were due on point duty until the after-the-show crush seventy minutes away.
Almost more significant still, if one were seeking a reliable eye-witness, Commissionaire George Wardle had just stepped down into the staff room of the ‘Porch’ for his mid-evening pint and sausage and so was not on duty outside the famous old restaurant which faces the Duke of Grafton’s Theatre and the dark entrance to Goff’s Place which runs down beside it.