I'm not aware of a tool that lets you directly read a log backup file. I'm sure there's a way to do this (for example, Red Gate has a tool that lets you read a full backup file and use it to compare data & structure to a database), but I have never seen a tool that does it. The only way I can think of to even get a good guess would be to do a restore to a point in time using the log backups you have and see what has been happening on the system that way.