Complex sentence: It was set ablaze and destroyed on 23 January, either as an agreed precaution against discovery or as an unauthorised act by Quintal--in either case, there was now no means of escape.
Split into simpler sentences: It was set ablaze and destroyed on 23 January, either as an agreed precaution against discovery or as an unauthorised act by Quintal. In either event, there was now no means of escape.