Firstly, what a nightmare for you !!
My DS2 is also 10 months old and now sleeps 12 hours a night and also has 2 daytime naps, one in the morning & one in the afternoon, of between 1-2 hours each.
IMO, the answer is leave him to cry (shock, horror - what a bad mother!!)
I found that when DS1 was a baby, if I let him fall asleep in my arms and then put him down he would wake up crying after a few minutes and not settle again. However, when I started to put him to bed awake, and left him to cry he would fall asleep by himself after 10-15 mins or so, and he would more often than not, wake up happy (unless he had a dirty nappy!!).
With DS2, I always put him to bed awake. He may cry for a little while sometimes, but its just a tired cry. I have had to be strong and leave him to cry (unless he gets really distressed).
Also, does your DS have things he can play with in his cot ? Mine has soft toys, rattles and a mobile which he loves.
Sometimes I don't even know he's woken up until I see him on the video monitor playing with his toys!
Maybe you could try putting him to bed at the same times, awake, for a few days and see how it goes, but let him cry. Don't forget, babies will always try their luck in the hopes that you will come and get them if they scream loud enough. You just need to try to be strong so you can get him in a routine before you go back to work.
Good luck, and please let me know how you go.