Where does the climax in The Chrysalids begin?

Remember that the climax in terms of the structure of the
plot of a novel is defined as the key scene in the story - that tense or exciting or
terrifying moment when our emotional involvement is greatest. During the climax we learn
what the outcome of the conflict is going to be. The climax is also the penultimate part
of the plot structure coming as it does just before the
resolution.

So, when we think about this great novel, for
me the most tense, exciting and terrifying moment comes towards the end of the novel in
Chapter 14 and 15. What we see is a massive collision of all the different parties in
the novel with David, Rosalind and Petra caught in the middle. Having fled Waknuk and
having sought safety in the Fringes, we find out that in a sense they have gone from the
frying pan into the fire. David's uncle wants to kill David and keep Rosalind for
himself to breed children. They clearly have not found the safety they wanted. However,
at the same time, David's father is heading an armed force that is invading the Fringes
to capture David and Rosalind and also kill as many "deviants" as possible. But, as if
this was not exciting enough for us, we are also desperately waiting the arrival of
Petra's friend for Sealand, who is coming to help David, Rosalind and Petra escape.
Phew! Are you sitting on the edge of your seat yet? You should be! The resolution of
course focusses on how these various conflicts are played out and ended, leading to the
end of the novel.