Start a new game and select "Inner Light" as your mystery.
This mystery, as with Power of Three, mostly plays out by itself and is narrative in structure. You cannot make wrong choices in this mystery, so choose as you wish - pretend this is a Telltale game! It didn't trigger until Sol 80 for me, and may have been caused by the expansion of my colony's population.
You'll need to research Dream Simulation (Breakthrough) when it comes up. It's pretty cheap, needing only 1000 research.
As the mystery develops, the game will assign a Dreamer trait to colonists. You will be able to teach it in schools. Dreamers will pass out when Mirages occur (randomly) and the number of dreamers who are asleep seems to be what moves the mystery on. You should build a dome or two and fill it with nurseries and schools teaching the Dreamer trait as soon as you viably can. Set the dome's filter to port in children born across your colony - and be sure to set every other dome to reject kids to force them to move. Continue expanding your colony and ensure each dome has a high comfort to promote procreation.
Eventually, the mystery will say you can treat Dreamers in Sanatorium to remove the trait. Don't do it.
You need large numbers of Dreamers to finish the mystery. I had 532 colonists by the end of my mystery run.