Taut. The set up was well done to provide the last minute coming together of different types of people. The mix of personalities and how they switch alliances so easily is less believable, but under stress is actually quite real. Survival is a great motivator. The science is junk, in that nearly all living things would be killed by such an event when the sun/gamma rays penetrate them. A focused burst from a nearby star in super nova would be a better explanation, but you lose the "night" factor and staying in the 'shade' of such a burst would be an extra math challenge to work out as they run from being exposed. Damaging solar flares have happened in human history ( google the Carrington Event ) but that was magnetic disruption causing conducting metals to heat up....in a time when telegraph lines and railroads were where most damage was noticeably done. Gamma rays...not so much.