Eason Chan’s 28th album (and 17th in Cantonese) is a brief yet intense listen that packs the full spectrum of emotion into soaring, larger-than-life tracks that show off the Hong Kong native’s still-robust vocals. Chan said in interviews around The Key’s 2013 release that its first track, “主旋律 (The Main Theme),” presented him with one of his greatest vocal challenges; composed by C.Y. Kong and Lesley Chiang, it’s a goth-rock opera in miniature, with Chan’s voice dipping into the lowest reaches and vaulting to the very top of his register as he sings about the parallels between love and music, strings cresting and pianos crashing around him as he thinks about a ships-passing interaction with someone for whom “the time isn’t right.”  “主旋律 (The Main Theme)” is a wild opening salvo, but the next two tracks match its heady heights, with Chan commanding a sonic maelstrom on “告別娑婆 (Goodbye Saha)” and digging into darkly hued midtempo rock on the swaying “斯德哥爾摩情人 (Stockholm Lover).” Although the music gets more delicate on tracks like the fluttering “失憶蝴蝶 (The Butterfly Effect)” and the serene “床頭床尾 (Head End, Foot End, Bed Ends),” Chan’s fervency remains, his voice sounding draped in velvet as he mulls over the way love can be fleeting on the former track and retells the ups and downs of a long-lasting couple’s relationship on the latter. “阿貓阿狗 (Cat and Dog),” which closes the album, swings between hushed verses and a raging chorus, with the singer breaking down the fallacies that influence others’ perceptions of success. The Key seethes with intensity musically and lyrically as Chan leans into full-throttle emotionalism and lets his listeners eavesdrop on his tumultuous inner monologue while he ponders life’s big questions.