Here you may find the answer to Sherlock holmes - I will sent you a train with a lock on it the secret documents are there.
(the train arrived)
Robbers - oh no it is a high tech lock.
Agent Chet- watson but we don't have a key to open this lock too how will we get the secret information if sherlock sends the key the robbers will take it.
Watson - do not worry we have a lock of our own.
Agent Chet - I on't understand you.
Watson - Come here i will tell you sherlocks plan.
( a few hours later )
Watson - atlst we got the documents!
What was Sherlocks plan? riddle.