The answer to the question posed by the title, presuming it isn't rhetorical, which since it is a detective story (nominally at least) one must presume not, is a destination that you gradually come to feel you might never quite satisfactorily arrive at - much like the end of this sentence. The reason why you might have serious doubts about ever discovering the whereabouts of Harold Absalon is due to the elaborate, circumlocutory, tortuous and frankly digressive processes of the person charged with discovering the whereabouts of the Mayor's missing transport advisor, Marguerite (the detective that is, not the transport advisor, who is indeed, or at least up until recently was (which doesn't suggest that he is dead, although this could be one eventuality) the aforementioned missing Harold Absalon), but the meticulous and indisputable logic of Marguerite at least points to a certain thoroughness in the investigation. So, Whatever Happened To Harold Absalon? You might well ask...
Whether you get there or not (it's worth taking all eventualities into consideration), you will at least enjoy the process (or possibly not) of the entertaining (or otherwise) diversions, digressions and deliberations of the thought processes of Marguerite that, frankly, stretch the elasticity of time and its relation to space to lengths hitherto unexplored in any work of fiction that I have come across. Following his lengthy disquisition on the matter you are guaranteed at least to never take the term "public transport" at face value, but Simon Okotie's clever writing (one that my semi-parody here fails to adequately do justice to, at least in terms of how inventively funny it can be) is that you discover that even the most simple of everyday processes involve mentally and subconsciously sifting through a much more complex series of definitions and weighing up of alternatives that, were we to logically examine them all, would indeed drive one to distraction. In Marguerite's case (in more than one sense of the world), there's a fragile balance to be maintained that, as well as being filled with comically absurd possibilities, also has more serious implications. The devil is in the detail.
Whatever Happened To Harold Absalon? then is not a book to read if you are looking for a fast-paced crime thriller. Halfway through its dense 200 pages, Marguerite's sleuthing has only managed to see him get on a bus, having followed his suspect Mrs Isobel Absalon out of a hotel where she was meeting a friend, and to be honest, he doesn't get much further than off the bus during the remainder of the investigation. Considering the transport-related subject matter then, and noticing that it has ideally sized chapters of between three and six pages which is helpful in estimating whether you can get to the end of another chapter before your arrival at your destination stop without having to break-off in the middle of a cliff-hanging situation (chance would be a fine thing), I was also misled into thinking that this would be an ideal book to read on the bus. It's not - for a number of reasons, two of which I will enumerate below.
i) Whatever Happened To Harold Absalon? is not the kind of book to read in expectation of arriving at a predetermined destination but one which makes an unsettling number of diversions along the way (which, depending on your own personal experience of bus journeys, you might think makes it ideal material for reading on a bus, but I would beg to differ), the other, ii) is that people tend to look at you strangely if you smirk a lot while reading a book, or worse, commit the social (transportational?) faux-pas of actually laughing out loud to yourself. You might find yourself doing this quite a lot reading Whatever Happened To Harold Absalon?, so choose your time for reading wisely and enjoy.