Complex sentence: Nyssa and the Doctor are reunited with Tegan while battling against Omega in Amsterdam and on Gallifrey, help Tegan battle her inner demons as personified by the Mara, and meet the Doctor's old friend and ally Brigadier Lethbridge-Stewart.
Split into simpler sentences: Nyssa and the Doctor are reunited with Tegan while battling against Omega in Amsterdam and on Gallifrey. They help Tegan battle her inner demons as personified by the Mara, and meet the Doctor's old friend and ally Brigadier Lethbridge-Stewart.