Theory:

GERRARD: (pleasantly) Why, this is a surprise, Mr— er —
 
INTRUDER: I’m glad you’re pleased to see me. I don’t think you’ll be pleased for long. Put those paws up!
 
GERRARD: This is all very melodramatic, not very original, perhaps, but…
 
INTRUDER: Trying to be calm and — er—
 
GERRARD: ‘Nonchalant’ is your word, I think.
 
INTRUDER: Thanks a lot. You’ll soon stop being smart. I’ll make you crawl. I want to know a few things, see.
Explanation:
 
Gerrard was taken aback when he turned around and noticed the intruder. He hadn't expected someone to break into his house without his permission, that too with a gun. Gerrard sensed something was amiss. Despite this, he didn't express his anxiety and approached the situation coolly. He spoke pleasantly to the stranger, hiding his fear and anxiety and said that he was surprised to see him.
 
Gerrard's lack of fear of the stranger surprised the intruder. The intruder began to speak. To begin, the intruder sarcastically said he was glad to see Gerrard being pleased to see him without fear. He also said Gerrard wouldn't be pleased for long, which might mean two things. Gerrard would be horrified if he understood the intruder's motive, and he also knew Gerrard would be killed and would no longer be living.
 
The intruder then instructed Gerrard to raise his hands when he finished saying these things. Despite the fact that the intruder had Gerrard at gunpoint, Gerrard appeared calm, and his gesture showed his maturity and wit in dealing with a tough circumstance. He replied calmly to the intruder, noting that the intruder's behaviour seemed dramatic and not natural. The intruder did not care to respond but commented that Gerrard was attempting to maintain his calm and.... (the intruder was short of words and so didn't complete the sentence). Gerrard completed the intruder's sentence, which he had left unfinished. He concluded the intruder's thought and sentence by stating that the term the intruder was looking for was 'nonchalant'. The intruder wanted to say Gerrard was attempting to be cool and not exhibit anxiety.
 
As Gerrard finished the intruder's sentence, the intruder sarcastically thanked him and said he'd soon make Gerrard crawl, indicating that he may shoot Gerrard at any time. He then informed him that he needed a few details from him.
 
Meaning of difficult words:
 
S.No
Words
Meaning
1.
Intruder Someone who enters a place illegally 
2.
Melodramatic Behaving or reacting in an exaggerated way
3.
NonchalantBehaving in a calm and relaxed way
4.
CrawlTo move along the ground on your hands and knees
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.