The Imperial Daleks have a mothership in Earth's orbit and are trying to get the Hand of Omega. Unfortuantly they are the only ones as another group of Daleks are on Earth and they are the Renegade Daleks who are smaller and less powerful.
The Renegade Daleks do capture the Hand of Omega and Davros sends a shuttlecraft of Imperial Daleks to get it. The Imperial Daleks have a transmat system in the basement of a school and they are using the headmaster to find the Hand of Omega. Unfortuantly when he is caught by the Renegade Dalek's spy he is killed by the Imperial Daleks. Then a group of Imperial Daleks tried to kill Ace but the Doctor couldn't make them move so they were blown up.
After the Imperial Daleks land they leave the shuttlecraft and meet up with two Renegade Daleks who destroy two Imperial Daleks. Davros then sends in the Special Weapons Dalek which is the most power Dalek in history. The Special Weapons Dalek blows up the two Renegade Daleks and carries on to find the Hand of Omega. When they do find it the Special Weapons Daleks blows up all of the Renegade Daleks and takes the Hand of Omega back to Davros.
The Doctor does try to tell Davros not to use the Hand of Omega but Davros goes and uses it anyway. Unfortunantly when approaching Skaro the Hand of Omega destroys Skaro and its sun. All that is left of Skaro is ashes. Then the Hand of Omega returns to the mothership and blows it up killing all of the Imperial Daleks. Except Davros escapes just in time in his escape pod.
The Imperial Daleks appeared in:
Season 25: Remembrance of the Daleks