When do the the characters from the book The Compound enter the compound

In the book The Compound, the characters enter the Compound during a "nuclear attack" at the beginning of the book. Eli's brother and grandmother do not enter, and are left behind.

The characters from the book " The Compound" enter the compound during a nuclear attack. The compound is lavish and seems to be located three stories under the ground. The family entered the compound for survival purposes or that is how their father made them believed however Eli discovered something suspicious and inconsistencies from his father. He knew there is something wrong and that he needs to get out but he knew his father was the only one who knew the code to leave the compound.