Complex sentence: Susan is eventually sent to retrieve anti-radiation drugs from the TARDIS, the Doctors realizes this was what the box contained, where she encounters a second species, the Thals, who used to be at war with the Daleks.
Split into simpler sentences: Susan is eventually sent to retrieve anti-radiation drugs from the TARDIS, the Doctor realizes this is what the box contained. Susan encounters a second species, the Thals, who used to be at war with the Daleks.