In responding to the A.C.L.U. lawsuit, the corrections department argued that there's no such thing as ''sensory deprivation'' in the solitary unit, and that it's not even ''solitary'' -- not, at least, in the classic sense of being the kind of ''hole'' in which Hollywood convicts spend so many movie minutes. In the cells it is possible to communicate with the inmate next door by lying with your face on the floor next to the sliding door and talking through the two-inch airspace underneath. This is why that area of all the cells seems a little shinier than the rest. You can also send notes down the tier by ''firing a line,'' a practice forbidden by the rules but tolerated by the guards, unless they choose not to. You do this by unraveling a nylon sock and tying the 20 feet or so of thread to an envelope containing a heavy object, like a bar of soap, than scaling it down the tier through the space below the door.

All that said, there remains a considerable amount of solo time. ''There's only so much you can do in a cell when you're locked in for 24 hours,'' Charlie says. ''You can pace. You can write letters, you doodle. If you got a TV, you watch TV, if you got a radio, listen to the radio. I haven't had a TV or radio since March 23, 1994.''

For diversion he seeks out the small fissures of prison life, looking for situations over which he can exert some control. ''Until recently, I was on tier C-2 -- that's where they put guys who 'rip out,''' he says, using the prison term for going berserk. ''When I take a shower there, I leave the water on just a little bit so in my cell I hear the dripping. 'Plip, plip, plip.' It drives the other prisoners crazy, off the wall, but I love it, because, you know why? Because, before I came into prison I used to go to Mount Washington hiking and camping, and I liked to go into caves and crevices where there'd be dripping water. I'd stay there for hours.''

During his better moods, he runs over the happy memories he can scrape together from his life on the outside. The only thing Charlie was good at in school was art -- so good, in fact, that once in high school he had his pictures selected for a student exhibit at Boston's Museum of Fine Arts. ''I think about how in the ninth grade I used to skip classes and go down to the art class, Mrs. Gunch's class,'' he says with great enthusiasm. ''She was, like, an older lady, and I loved her. She would bring in homemade apple pie, and she'd lock me in a back room so I wouldn't get caught and get me all the art supplies I needed, and I'd sit there and draw. Whenever I wanted to, I knew I could go down there and she'd always take care of me.''

His art supplies are now limited to a black Papermate pen and the 50-page lined writing pad that inmates are issued once a week. He'll cut up parts of his bedsheet if he needs canvas for a major production, something that earns him additional sanctions for destroying prison property. To get different shadings, he dilutes the ink with water and also files the brass tips of the pens on the floor so the ink flows around them in different thicknesses. He then removes the tips and keeps five or six of them honed in different fashions, which he fits to the new Papermate whenever it arrives.

Sometimes, if he is thinking positive thoughts, he'll reproduce nature photographs and pictures of birds from The Boston Globe, which he is allowed to subscribe to. Other times the images come out a little darker. When he talks about the dark things, his speech becomes disjointed and he flashes a manic smile, something like Jack Nicholson's in ''The Shining.'' ''I'll be honest with you, I hate the prison administration with a passion, and I would have to say, half my day, if not all, I lay back in bed, just close my eyes, and other prisoners say sometimes I talk to myself, but I'm not aware of it, and in that state I get enraged sometimes, and I only think of getting my animosity out, fantasizing hurting people, thinking what I can do to somebody. Sometimes, lots of times, I fantasize about cutting someone's head off, cutting their heart out, and if I got nothing to do I take myself out on a piece of paper. I do murder scenes, stabbing scenes, shooting people in the head. The prison shrinks started confiscating these kinds of drawings and putting them in my file. So now when I do one, I flush it down the toilet.''

Because he reacts in a volatile manner to the slightest provocation, Charlie provides an easy target for guards who want to get his goat. He complains that they sometimes shake up the food in his meal containers so it's all mixed together, then draw a smiley face on the cover. Or when he comes back from the rec cage he'll find that someone has poked a finger in a piece of food he had saved from his meal.