Solution to 17D has been deliberately left unsolved and is to be answered only by a non-regular / novice commenter, with proper annotation. Those who have answered earlier in the week, please give others a chance.
Open for anyone to answer, if not solved by 1 PM.
ACROSS
1 PM comes to grip with a druggie without work and his method of working (5,8) MODUS OPERANDI {MOD{US{{OP}ER}{AND}I}
10 Slammed as the little devil played a role (5) ACTED impACTED
11 With home study make true agreement (9) INDENTURE {IN}{DEN}{TRUE*}
12 Rage about one going underwater — it's highly corrosive (4,5) AQUA REGIA {REG{1}A*}<=>{AQUA}
13 Sweep opening, take time off for golf (5) DEBUG DEBU(-t+g)G
14 The German drink will subside (3,4) DIE DOWN {DIE}{DOWN}
16 Good natured, is nice to back some one in the group (7) INSIDER [T<=]
18 Next to undress — questions follow revelations (7) EXPOSES {nEXt}{POSES}
24 Sailing, generally (2,3,4) IN THE MAIN [DD]
26 Initially, no objection certificate to use radio not allowed late in the night (9) NOCTURNAL Acrostic
27 Speak for zero value (5) ORATE {O}{RATE}
28 I get a front man out breaking (13) FRAGMENTATION*
DOWN
2 Starts offering basic training — it's impolite to interfere (7) OBTRUDE {Of...g}{Ba..c}{Tr...g}{RUDE}
3 Experiences of active end user taking leave (9) UNDERGOES {END+USER}* over {GO}
4 Start off planting being in debt (5) OWING sOWING
5 Adorable, getting attention in conclusion (9) ENDEARING {END{EAR}ING}
6 Covered new roof within a day (5) AWNED {A}{NEW*}D} Roof as Anind?
7 Pounded back of head and massaged (7) DRUBBED {heaD}{RUBBED}
9 Not even greying beard can be contrary to a radiation detector (6,7) GEIGER COUNTER {GrEyInG+bEaRd}{COUNTER}
17 "Room for suspicion", they say, when disoriented (6-3) S?A?E? O?T ()
19 Spectacular shot, showing no lust for a safety vehicle on track (4,3) PACE CAR sPECtACulAR*
23 Suspended second breather (5) SLUNG {S}{LUNG}
25 Washroom — not one available for renting (2,3) TO LET TOiLET
Reference List
Work = OP, Time = T, Golf = G, Day = D, With = W, Second = S