It also marked the return of several past associates and companions of the Doctor, including Sarah Jane Smith. Martha Jones, Jack Harkness, Harriet Jones and Rose Tyler. It served as a "cross-over" between Doctor Who and its two current spin-off series, marking the first appearance in the series itself of several characters introduced in those spin-offs; namely, Ianto Jones, Gwen Cooper, Mr Smith, and Luke Smith. The episode also featured the death of Harriet Jones and the loss of the Valiant in ill-fated meetings with the Daleks.