▁to ▁depart ▁in ▁his ▁T ARD IS , ▁allowing ▁himself ▁and ▁Per i ▁to ▁handle ▁the ▁situation . ▁Se par ately , ▁the ▁Doctor ▁and ▁Per i ▁learn ▁from ▁a ▁group ▁of ▁boys , ▁part ▁of ▁Magn us ' ▁bre eding ▁program ▁and ▁led ▁by ▁V ion , ▁that ▁there ▁is ▁a ▁prop he cy ▁of ▁a ▁revel ation ▁that ▁will ▁change ▁Magn us ' ▁society ▁for ▁the ▁better , ▁her ald ed ▁by ▁the ▁Doctor ' s ▁arrival . ▁ ▁The ▁Doctor ▁is ▁forced ▁to ▁show ▁R ana ▁and ▁Sil ▁how ▁to ▁use ▁his ▁T ARD IS ▁when ▁they ▁hold ▁Per i ▁host age , ▁but ▁limits ▁their ▁travel ▁to ▁only ▁a ▁few ▁hours ▁ahead . ▁Left ▁behind , ▁the ▁Doctor , ▁Per i , ▁and ▁V ion ▁discover ▁that ▁a ▁large ▁number ▁of ▁Ice ▁War riors ▁have ▁been ▁hiding ▁under ▁Magn us ' ▁ice ▁caps , ▁and ▁have ▁plant ed ▁nuclear ▁explos ives ▁around ▁the ▁planet ▁aim ed ▁to ▁push ▁it ▁out ▁of ▁orbit ▁and ▁farther ▁away ▁from ▁its ▁sun ▁as ▁to ▁make ▁its ▁overall ▁climate ▁hosp itable ▁to ▁the ▁Ice ▁War riors , ▁despite ▁the ▁loss ▁of ▁life ▁on ▁the ▁surface . ▁They ▁encounter ▁the ▁surv iv ors ▁of ▁an ▁expl oration ▁team ▁from ▁Salv ak ▁that ▁had ▁come ▁to ▁offer ▁the ▁c ure ▁to ▁the ▁virus ▁out ▁of ▁comp ass ion ▁with ▁no ▁plans ▁to ▁in va de , ▁but ▁instead ▁were ▁caught ▁by ▁the ▁Ice ▁War riors . ▁With ▁their ▁help , ▁the ▁Doctor ▁and ▁his ▁al lies