London. Nine million people. Two-hundred-and-seventy tube stations. Every day, thousands of chance encounters, first dates, goodbyes and happy ever afters.

And for 20 years, it's been where one man and one woman can never get their timing right.

Jennifer and Nick meet as teenagers, and over the next two decades, they fall in and out of love with each other. Sometimes they start kissing. Sometimes they're just friends. Sometimes they stop speaking, but they always find their way back to each other.

But after all this time, are they destined to be together or have they finally reached the end of the line?