The Eagle of the Twelfth by M.C. Scott

This is the third in a series of novels telling of the career of Pantera, by appointment spy and assassin to the Emperor Nero.
The novel opens as Pantera has been sent to Parthia disguised as a merchant and accompanied by two soldiers he has picked  from the Legion Fifth Macedonica, Cadus a centurion and Demalion a squadie with a knowledge of horses.   In Parthia the King Vologases has been overthrown by Vardanes  who, to consolidate his reign, was pushing for a war with Rome.   Pantera has been sent to effect regime change.   He does.
On their way back to rejoin General Corbolo Pantera reveals that he has been ordered to return to Britain but that Cadus and Demalion have been transferred to the Twelfth Fulminata a Legion with a terrible reputation.   To make matters worse the Twelfth has been removed from the command of General Corbolo and given to Gallas, a politician whose only concern is his own advancement.   Corbolo has struck a deal with the Parthians that no Romans would cross the Euphrates but Gallas promptly takes the Twelfth across which leads to them being virtualy wiped out.
Demalion, now a centurion, is one of the few survivors and is instrumental in rebuilding the Legion but no sooner have they accomplished this than they are put under the command of another incompetant and lead to anihilation in Judea and this time they face the shame of losing the Eagle.
During the battle who should turn up advising the Hebrew King but Pantera.   Has Nero's number one agent turned traitor or are the plots becoming deeper and darker?   Will Demalion and the one other survivor of the massacre be able to rescue the Eagle?   Will Pantera come to their rescue?
Manda Scott has written another ripping page- turning yarn about the era that I love and the best part is that the next volume in the series has just come out!