Drawing on the adventures of his recent book Overnight and acclaimed Radio 4 series, Only After Dark, Dan Richards tonight shares small hour stories from North Sea ferry crossings, the night mail, search and rescue helicopter missions, the service of the NHS and St Mungo's outreach workers, and Edinburgh's vespertine wildlife ... among other twilight wonders. Feel free to bring a hot drink as you walk. Meeting point: Collective, City Observatory. Check back here for more details.