Fic Title: Something I Ate
Why This Must Be Read: This is the first LTM fic I ever read, and it still stands up today. It's set between season 1's Better Half and Undercover, and the author just gets these two characters. Gillian is unwell and Cal takes it upon himself to look after her; it's filled with moments that make you melt. It's so in character; I can't recommend it enough.