Here's a breakdown:
1. The setup: Helen Stoner is terrified of a deadly, speckled snake that her stepfather keeps in his room. She believes it is responsible for her sister's death and fears it will kill her next.
2. The confrontation: After Sherlock Holmes discovers the snake's presence and its method of attack, Helen is trapped in her room with the snake ready to strike.
3. The climax: The snake approaches Helen's bed, but she has placed a metal poker nearby. She uses it to kill the snake before it can bite her.
4. The resolution: Holmes arrives just in time to witness the snake's death and Helen's victory. He arrests the stepfather, who confesses to the crime.
This moment marks the culmination of tension and danger built throughout the story. Helen's bravery in facing her fear and using her wits to outsmart the deadly creature is the defining moment of the climax.