The Tardis brings the Doctor, Donna and Martha to the planet Messaline. There they meet some human soldiers who take a tissue sample of the Doctor and grow a new soldier from his DNA in seconds. The Doctor doesn't know what to say when he meets his daughter for the first time. When the Hath arrive, a race the humans fight against, Jenny, the Doctor's daughter, activates a detonation and Martha ends up on the side of the Hath when the tunnel collapses. Donna and the Doctor are brought to General Cobb, the leader of the humans, and he tells them that this war is going on for generations. They are searching for the Source, a weapon that shall help them to defeat the Hath. The Doctor, Donna and Jenny try to reach the Source before the General and hope to avoid a war this way. When they've reached the rocket the humans and Hath came with they meet Martha again. Soon it becomes clear that the ship arrived on the planet just seven days ago but will this knowledge help the Doctor to stop the killing?
I think it's great to have Martha in another episode with Donna and the Doctor but others may see this differently. I just like her character and the things she adds to the show. She is just someone who wants to help people and she is not afraid to help when there is an injured alien in front of her. Donna is often like a conscience for the Doctor and helps him to see thing differently in her own special way. I really liked the idea of the Doctor having a daughter and it's so sad to see him loosing her again in the end. Well, he doesn't know that she is still alive though and I haven't given up the hope that we will see Jenny again in another episode. That would be really cool. It seems that the humans and Hath will work together now and I think that's a good ending to this story. At the same time it was sad to see Martha leave again but we still have Donna, so onwards to the next adventure.