series of 3 encounter ideas

[The Outlaw Josie Whales]

I would like to later this week run a quick mini adventure for 6 1st level characters that is combat focused. Specifically I am looking for ideas for 3 interrelated encounters which get more difficult culminating in a "big boss" type ending (although it doesn't have to be a solo) I would like the series to be challenging and the creatures to not be completely random, ie as above related in some way.

thanks for any help.