"Nightcall" by London Grammar seems to be an emotional expression of love and desire. The singer is reaching out to someone she cares about, offering a nightcall to express her feelings. She wants to take this person on a journey through the night, down the hills, to share something that they may not want to hear but should not be afraid of.
The outro repeats the refrain and emphasizes that the nightcall is a way for her to share how she is feeling with this person. The melody and delivery of the song gives it a melancholic and introspective tone, adding to the emotional depth of the lyrics.