reappearing in april 2008's series four premiere, "partners in crime", donna has become dissatisfied with regular life and more interested in the bigger picture. she regrets declining the doctor's offer and has been investigating unusual phenomena in the hopes of finding the doctor for some time. when investigating miss foster and adipose industries, the londoner and the time lord are finally re-united. she expresses her regret to the doctor for not joining him and after stopping foster's plans to convert the whole of london into adipose children she joins him in the tardis as a regular companion. she makes it explicit, however, that she has no romantic attachment to him as martha jones and rose tyler did.