Don't know this specific one, but have you ever seen "The Limits" by Tracey In Peril? Similar theme. Young woman puts herself in several or cajoles her boyfriend into putting her into severely risky situations like locking herself into a safe where she will be stuck unless/until her boyfriend finds a note and figures out the riddle on the note and finds her, etc. I can't find a link for you (my notes say I found it on BDSM Library but I can't find it there now) and I can't post someone else's (excellent) work, but if you were interested there's probably an easy way to get it to you....