Chakotay falls in love with a lady from a race who produce a pheromone that affects the memory.
Themes of falling in love and the consequence associated with memory erasure of the relationship was done very well in 'Eternal Sunshine of the Spotless Mind', but although the sci-fi premise here is similar, the love story does not work for me.
I do not think it is badly written or acted (as some have suggested), as there is only so well you can portray two strangers falling in love in one episode. It suffers from the usual issues that blight love stories for regular characters. I personally could not invest in the relationship and they never convince me of the love. I spent a large part of the episode suspicious of Kellin and her motives because they are hard to take at face value given the twisting nature of so many Trek plots.
Robert Beltran and Virginia Madison do a great job with the material. In one scene in particular, their chemistry is great, but the script calls for Chakotay to suddenly decide that he is in love which is difficult for any actor to pull off.