In June 2007 Lance was working as the head of human resources at H.C. Clements, where Donna had just landed a temp job. His offer of a cup of coffee quickly turned into a romantic relationship, at least for Donna, who pressured him into marriage (though Donna later claimed he pressured her). Their wedding was scheduled for 24 December 2007.
Unbeknownst to Donna, Lance had been working for the Empress of the Racnoss for at least six months. At the Empress' behest, he dosed her with dangerous Huon particles over this period, intending for his Huon-saturated bride to provide the energy that the Empress needed to resurrect her race. In reality, Lance thought Donna was stupid, claiming she couldn't even point to Germany on a map and thought "the height of excitement [was] a new flavoured Pringle", and that he only agreed to marry her to prevent her running off; he felt he deserved a medal for putting up with her for all that time. He saw the human race as nothing, and was promised the chance to "go out there, to see it, the size of it all".
When the Tenth Doctor rescued Donna, the Empress betrayed him, force-feeding Lance with a high concentration of huon particles. He soon after met his end in the hungry jaws of her children. Donna later claimed, at first, he deserved it, though soon admitted that he didn't. (TV: The Runaway Bride)