Following a near accident, the boys are invited to the principality of Varania, to help Prince Djaro discover the location of the fabled Silver Spider, which has been stolen. Bert Young, a secret service agent, also recruits them as it’s feared the Prince Regent is plotting to overthrow Djaro and make Varania a crooks paradise. Told at breakneck pace, this has high adventure, mystery, daring escapes, a couple of bumps on the head for Bob and a thrilling climax. Superb stuff.One of the last books in the series I bought, I found this by chance on a stall at a car boot sale in Kettering. I got the 1979 edition and loved the cover (below left). Years later, when I was making the bulk of my collection the 1982/1983 edition printings, I got hold of that version of this (below right). I love that cover as well. So, which is best?