Half-Life Episode Two begins exactly where Half-Life ended, after accepting the job agreement with Gman Gordon freeman is sent back to the Black Mesa Research Facility, why? Its up to you to find out.
This is the source code for the last public version of the Trinity rendering engine, version 3.08f. I'm uploading it here for future reference, in case any other links die down, this version is almost entirely outdated, it has since been rewritten in many aspects and it's successor will be featured in the HLEP2 beta, and the full release, once it does come out.
Full Source code with detailed usage instructions, nothing Trinity users haven't already seen.