、。
By this time tomorrow, I'll be in London.
Literal
Tomorrow [possessive-の] this-about-time [until-までに], I [topic-は] London [in-に] be probably.
までに = 'by the time of X' (deadline), as opposed to まで ('up to X'). The verb いる ('to exist, for animate beings') is the existence verb — Japanese uses different existence verbs for animate (いる) and inanimate (ある) subjects.