Theory:

INTRUDER: (preparing to shoot) As I said before, this conversation bores me.
 
GERRARD: Don’t be a fool. If you shoot, you’ll hang for sure. If not as yourself, then as Vincent Charles Gerrard.
 
INTRUDER: What is this?
 
GERRARD: This is your big surprise. I said you wouldn’t kill me and I was right. Why do you think I am here today and gone tomorrow, never see tradespeople? You say my habits would suit you. You are a crook. Do you think I am a Sunday-school teacher? The game’s up as far as I’m concerned. Things went wrong with me. I said it with bullets and got away. Unfortunately they got one of my men, and found things the fool should have burnt. Tonight I’m expecting trouble. My bag’s packed ready to clear off. There it is.
Explanation:
 
The intruder was unwilling to listen to Gerrard and was prepared to shoot him. As he had stated previously, he informed Gerrard that their discussion was boring. However, Gerrard advised him not to be a fool, as murdering Gerrard would likely result in death rather than a peaceful existence for the intruder. He intended to inform the intruder that Gerrard's true identity would certainly get him in trouble again. In addition, Gerrard warned him that if he exploited Gerrard's (Vincent Charles Gerrard) identity, he might be hung to death. The intruder was taken aback and wanted to know how his (Vincent Charles Gerrard's) identification would impact him.
 
And it was Gerrard's turn then, as the intruder had believed Gerrard's words. Gerrard continued to speak. He told the intruder that it was his big surprise. He claimed himself to be right, as earlier, he told the intruder that he would not kill Gerrard.
 
Gerrard utilised this opportunity and started to weave a plot around his mysterious life. He explained to the intruder that the reason behind Gerrard living a mysterious life, avoiding people, and engaging in unusual activities that suited the intruder was due to the fact that he was a criminal and a killer.
 
Gerrard said he was a criminal, not a good man like a Sunday-school teacher who teaches God's teachings to people in order to alter their lives for the better. When he killed someone with a gun, his game was finished. After then, one of his accomplices was arrested by the cops and they had proof against Gerrard. Gerrard had anticipated the police raiding his house that night in order to arrest him, so he had packed his belongings and was ready to go.
 
Meaning of difficult words:
 
S.No
Words
Meaning
1.
Clear offTo go away
Reference:
National Council of Educational Research and Training (2006). Beehive. If I Were You - Doughlas James (pp. 138-144). Published at the Publication Division by the Secretary, National Council of Educational Research and Training, Sri Aurobindo Marg, New Delhi.