In The Proxima Nexus, the fifth book of the Second World Series, Earth and Mars are recovering from impacts of Shiva debris. The Perseus Mission has reached planet Thelus in the Proxima Centauri star system using the faster-than-light X-drive system technology mined from a Thelud artifact. The artifact, The Box, was found by Sofi and Alex Ivanov in an extinct comet. Hoping to find the mysterious Thelud on their home planet, our travelers discover that the Thelud have abandoned Thelus and emigrated to another star system and the planet Inphos.

Stella Ivanov-Weidman and her brother Andrei Ivanov play a pivotal role, along with the CASSI AI system, in mining more Thelud technology from an artifact known as The Monolith. As their settlement grows, they decide to split into three groups. One group is to take advanced Thelud technology back to Mars, one group is to stay and further explore Thelus, and the third group is to follow the Thelud to Inphos using a new ship they have constructed with more advanced Thelud technology. What truths will they discover about the mysterious Thelud when they finally reach Inphos?