The China Toy is the series finale of SJA series 4, which says goodbye to luke and K-9, it aired on the 23rd November 2010
"what happened to your friend, Mr. Luke Smith, Gran?" said Janey Song, Great-Great-Great-Great-Great Grandaughter of Professor Maria 'River' Song, River said, "I never knew, He just disappeared, i need to find him, him and the doctor."
Ding Dong! Sarah-Jane Smith's door bell went off, she answered it, to find a young woman, about 25, named river song, she said, "Smith, We Need the China Toy!"
In this action-packed season finale, The Doctor makes a guest appearance along side the realisation of who River Song is, why is Luke being trapped in the China Toy, why is K-9's Digi-X failing and why Sarah-Jane must make a life-changing decision.
Elizabeth Sladen as Sarah-Jane Smith
Thomas Knight as Luke Smith
Yasmin Paige as Maria Jackson/Young River Song
Alex Kingston as River song
Matt Smith as The Doctor
John Leeson as K-9 (Voice)
Anji Moranda as Rani Chandra
Daniel Anthony as Clyde Langer
Tallis Mills as The China Boy-Guard