Showing Imagines (Imago, Book Two) by N. R. Walker

Jack Brighton and Lawson Gale have been together for six months and are very much in love. Lawson’s work ensuring the survival of the Tillman Copper is as demanding as ever, and Jack’s work with the regeneration of the bushfire-ravaged national park is just as hectic.
When Jack suggests they take a short trip, Lawson agrees. But then he is offered a two-week research position in tropical Queensland to help determine why the Ulysses butterfly is on the decline. Figuring they could combine work and pleasure, Jack and Lawson go on their first vacation together.
Working alongside renowned professor Piers Bonfils isn’t easy. But personal and professional differences aside, Lawson is offered a more permanent role in Queensland. Torn between his new life in Tasmania with Jack and a dying species of butterfly he feels compelled to save, Lawson has to decide where his fate lies.
But fate changes the rules. On a research expedition into the depths of the rainforest, suddenly it's not only the butterflies’ existence that hangs in the balance.
A butterfly’s life cycle never changes. From larvae to imago, their course is plotted by design. Jack and Lawson need to determine where they stand, if they live through it. Because the only thing more incredible than one imago is two.