Watch Blue Murder at St. Trinian's for Free: How to Stream the Movie Online at 123Movies. . With their headmistress under lock and key in her majesty's prison, the St Trinian's girls find themselves under the protection of the army. However, when the sixth form take a fancy to winning a trip to Italy through means fair or foul, the army discover this is one battle they can't win. Let loose in Europe, it is not long before St Trinian's have succeeded in endangering European relations.