The new content sees Lara Croft having to explore a decommissioned Cold War research base in Siberia. It is here where she will have to encounter possibly her greatest challenge, as the soldiers located here aren't human anymore. They're all killers out for blood due to an unknown infection that originates from the base, and it's your job to get to the bottom of it.
If you've already got the season pass, you can just download it for free, otherwise, it will be sold individually for $9.99. You can also see a bit of the content in action towards the end of the trailer featured above.