Time Bomb ( comic story ) Time Bomb was a Sixth Doctor comic strip published in " Doctor Who Magazine " . It dealt with some of the issues involved in the alteration of history . Summary . After a time cannon hits the TARDIS , the Sixth Doctor and Frobisher find themselves among a people who are disrupting time ' s correct path . Plot . Peri Brown has been dropped off in New York City to see the Dodgers play baseball . The Sixth Doctor and Frobisher are travelling in the TARDIS to pick her up when they are hit by a time cannon — technology only Gallifrey is supposed to have . To find and destroy it , the Doctor materialises the TARDIS near the cannon on the planet Hedron . The Hedrons have used the cannon to destroy all traces of genetic imperfection in their species . As the Doctor and Frobisher exit the TARDIS , they are captured by a robot , placed with the other genetic imperfections and hit with the time cannon . This sends them to prehistoric Earth . The TARDIS is also hit by the cannon and goes with them . The Doctor locates the cube of genetic imperfections and takes it to prevent it from contaminating life on Earth . However , before Frobisher and he can reenter the TARDIS , bodies of dead Hedrons begin to appear . It seems the Hedrons are continuing to use their cannon . Although he is desperate to prevent the Hedrons from contaminating Earth any further , the Doctor decides that he should pick up Peri in case she can help talk to the Hedrons . Materialising in New York City in the year 1986 , the Doctor and Frobisher find Earth controlled by sentient reptile s . Apparently the Hedrons ' genetic material has altered the course of life on Earth so that humans never evolved . The Doctor and Frobisher make a hasty retreat and return to prehistoric Earth to attempt to reverse the damage done by the Hedrons . While the Doctor mulls over the situation , Frobisher decides to grab a bite to eat , but before long a large aquatic dinosaur decides to eat him . Trying to rescue Frobisher , the Doctor grabs the nearest object and hurls it at the dinosaur . However , the nearest object is a sphere containing Hedron genetic material . It smashes open , causing the dinosaur to flee but also irreversibly contaminating prehistoric Earth . Angry that Frobisher has caused him to further contaminate life on Earth , the Doctor and Frobisher return to Hedron so they can at least destroy the time cannon and prevent it from doing any further damage to the universe . When they arrive on Hedron , however , they find that everyone has died through some terrible cataclysm . They find a recording from one of the last Hedrons and learn that the cause of the destruction was a spaceship that had crashed on the planet , releasing microbes and poisons which the Hedrons had eliminated and to which their immune systems had no defence . As it turns out , the origin of the deadly space ship was none other than the planet Earth . Thus , time had healed its own wounds and the genetic material that the Hedrons had banished from their planet had come back to them with deadly results . The Doctor destroys the time cannon and Frobisher and he take the TARDIS back to Peri ' s baseball game . As the Doctor exits the TARDIS he wonders if they will be able to sneak into the game without paying . This seems unlikely , however , as the TARDIS has materialised in the middle of the baseball field , much to the players ' confusion .