Political life has always been full of mysteries and secrets. The Zinoviev Letter led to the defeat of the first Labour Government in 1924. Was it genuine - or was it an early attempt to use 'red scare' tactics to bring down a democratically elected government? And if so, who sent it? The Prince of Transylvania received a pension from Charles II and a magnificent burial in Rochester Cathedral. But was he a prince or a con-man - and why was he so hideously murdered? Christopher Andrew and Gabriel Ronay investigate two political mysteries.