Terror Underground! is the third Astrosaurs Academy book in the series. In it Teggs and his friends are practising for a astro-jet flying display when Damona's jet crashes into Teggs's and both teams find themselves stuck underground in an icy cavern. But the gang have got more than just getting themselves out to deal with - there's a frozen war hero, some rotten raptors and some Giant spiders stuck in the cold too.