Complex sentence: After being interrogated by Grishin, he escapes with the help of Elena, and Sonia, who kills Grishin and takes his phone, which allows them to locate the FSB agents spreading the viruses.
Split into simpler sentences: After being interrogated by Grishin, he escapes with the help of Elena, and Sonia. Sonia kills Grishin and takes his phone, which allows them to locate the FSB agents spreading the viruses.