Alina and her friends staged an attack on the Apparat , because he was keeping them under ground in the tunnels.
After escaping from the tunnels, they were attacked by ravagers, but Nikolai found them and took them to his base in the mountains.
The Darkling attacked them in the mountains, but Alina and her friends were able to escape, because Baghra, the Darkling's mother, sacrificed her life for them
Alina and her friends went in search for the third amplifier, but when they found the firebird, Mal saved Alina's life and they found out that Mal was the third amplifyer, because he's a descendent of Morozova
Alina, her Grisha, and her Sun Soldiers suprise attacked the Darkling. Alina was forced to kill Mal, to use him as an amplifyer, to save everyone and kill the Darkling. Having all 3 amplifyers took away Alina's powers and dispersed it to others.
Tolya and Tamar brought Mal back to life, but they staged Mal and Alina's death, so that they could live together in peace for the rest of their lives.