After encountering the Fourth Doctor and Sarah Jane, he got involved with the Doctor's battle against Sutekh, who had reanimated the corpse of his brother, and even travelled briefly in the Doctor's TARDIS — which he described as being "like something by that novelist chap, Mr Wells!" — when the Doctor took him and Sarah to an alternate future Earth in 1980 to show the desolate world Sutekh would create if broke free of his bonds in 1911.
Lawrence originally refused to accept that Marcus was dead and tried to prevent the Doctor's attempt to break Sutekh's control. Later, he tried to reason with Marcus and remind him of his past. Although he seemed at first to be getting through to the real Marcus, the conditioning proved too strong. Marcus interrogated and then strangled Laurence. (TV: Pyramids of Mars)
The Scarman prior burned down that night following Sutekh's defeat and Laurence was believed to have been one of the casualties. According to one newspaper, the villagers speculated that one of Laurence's advanced scientific devices had caused the fire. (PROSE: Doctor Who and the Pyramids of Mars)