<human>: Can you provide a brief rundown of the text in within 3 sentences?

Okay this happened about 9 hours ago.

I am at university in the UK and live in a house of five. 

This morning, one of my housemates and I (both male) were the only two occupants around all morning and we had been watching TV in our front room for several hours. 

We both had lectures at 3pm and decided to go up to campus a bit early. So we go into our respective rooms to get our stuff (his is ground floor, behind the front room, mine upstairs). He calls for me to come down and there is a strong smell of cigarette smoke in his room (I am the only smoker in the house but we think nothing of it). We then proceed to go out the back door which leads to the garden, which has a utility room in it. We have a habit of locking the back door and hiding the key in there. So my buddy heads up to the back gate while I lock the door and go to hide the key.

I open the door and there's a dishevelled man in his late twenties sitting there smoking. I freeze and he abruptly gets up and runs past us out the garden. 

We had the police round and they checked with us. Nothing was taken which begs the question what was he doing...

Our interior walls are very un-soundproofed so I guess he was doing whatever in my friends room and heard us leaving so ran and hid.

The really scary part is that I was smoking in the garden a few minutes ago (0030 hrs) and the locked room within the utility room had been unlocked for the first time in the year we've lived here. So my guess (seconded by the police) is that he's been living in a small disused toilet we didn't know existed in our garden until tonight due to (we thought) the landlord locking it.
<bot>: the homeless man who has most likely been living in our garden has managed to start wandering round our house while we are obliviously watching TV.