Fics like Intervention

Upon his second ascension, an Immortal Daniel makes the decision to intervene in a bad situation, thus saving his son, reconnecting with his lover, and returning to a world he'd thought he'd left behind. An SG1/Highlander fusion with a stray Buffy character and a Harry Potter anchor. Spoilers up to and AU after: Stargate SG-1 season 8, Threads; Highlander season 6, Indiscretions; Buffy season 6, Once More with Feeling; the entire Harry Potter series. Intended for adult readers. Warnings: time travel, fluff, bad language, gay sex, and a whole lot of flashbacks (all entirely necessary to the plot, of course).

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